Co-composting of soybean residues and leaves in Hong Kong

Dynamics of co-composting of pineapple harvest and processing residues with poultry litter and compost quality

The production of pineapple generates significant quantities of harvest and processing residues, which are very little used. This study evaluates compost quality using pineapple residues and poultry litter. Five composting treatments were tested, varying following proportions of crown, pineapple processing wastes (PPW), pineapple harvest residue (PHR), and poultry litter (PL). Various parameters were analyzed, including pH, electrical conductivity, CO2 evolution rate, water content, organic carbon, nitrogen compounds, phosphorus, potassium, calcium, magnesium, copper, and zinc. Additionally, the perceptions of producers and processors regarding compost quality were gathered. Results indicated that microbial decomposition increased temperature, pH, CO2 release, and nitrogen content while reducing electrical conductivity and organic carbon. Composts demonstrated favorable characteristics for crop fertilization, with C4 (75% PHR + 25% PL) compost showing the best chemical properties. Producers and processors preferred the color, odor, and structure of C4 (75% PHR + 25% PL) and C5 (56.25% crown + 18.75% PPW + 25% PL) composts. Overall, composting pineapple residues with poultry litter yields composts suitable for plant fertilization, particularly C4 and C5 formulations, offering potential for sustainable waste valorization in agriculture.

Optimizing Straw-Rotting Cultivation for Sustainable Edible Mushroom Production: Composting Spent Mushroom Substrate with Straw Additions

In recent years, the optimization of straw-rotting formulations for cultivating edible mushrooms and the management of the resulting spent mushroom substrate have emerged as new challenges. This study aimed to investigate the composting of spent mushroom substrate produced from mushroom cultivation with various straw additions, under conditions where chicken manure was also used. Parameters measured during the composting process included temperature, pH, electrical conductivity (EC), germination index (GI), moisture, and total nitrogen content. Additionally, changes in nutrient content within the compost piles before and after composting were determined, and the variations in bacterial and fungal communities across different treatments before and after composting were analyzed using 16S rRNA and ITS sequencing. The results indicated that the spent mushroom substrate produced by adding 20% straw during mushroom cultivation was more suitable for composting treatment. The findings suggest that incorporating an appropriate amount of straw in mushroom cultivation can facilitate subsequent composting of spent mushroom substrate, providing an effective strategy for both environmental protection and cost reduction.

Recycling of Faecal Sludge: Nitrogen, Carbon and Organic Matter Transformation during Co-Composting of Faecal Sludge with Different Bulking Agents

This study investigated the effect of locally available bulking agents on the faecal sludge (FS) composting process and quality of the final FS compost. Dewatered FS was mixed with sawdust, coffee husk and brewery waste, and composted on a pilot scale. The evolution of physical and chemical characteristics of the composting materials was monitored weekly. Results indicate that bulking agents have a statistically significant effect (p < 0.0001) on the evolution of composting temperatures, pH, electrical conductivity, nitrogen forms, organic matter mineralisation, total organic carbon, maturity indices, quality of the final compost and composting periods during FS composting. Our results suggest reliable maturity indices for mature and stable FS compost. From the resource recovery perspective, this study suggests sawdust as a suitable bulking agent for co-composting with FS-as it significantly reduced the organic matter losses and nitrogen losses (to 2.2%), and improved the plant growth index, thus improving the agronomic values of the final compost as a soil conditioner. FS co-composting can be considered a sustainable and decentralised treatment option for FS and other organic wastes in the rural and peri-urban communities, especially, where there is a strong practice of reusing organic waste in agriculture.

Extent of degradation in three stage co-composting of fecal sludge and solid waste

Co-composting of fecal sludge (FS) and solid waste (SW) allows recycling of essential nutrients into agriculture thereby closing the nutrient circle. In this study, temperature variation, the mass balance of forced and passive aeration in the composting process, and the extent of degradation with different stages were investigated. The extent of degradation was determined through the different composting process in the first, second, and third stages with different mix proportion of fecal sludge. Four sets of the initial waste mixture were prepared using SW and FS. SW and FS were mixed at four different ratios for four sets namely 90:10, 85:15, 80:20, and 75:25 (SW:FS). Forced aeration and passive aeration composting tests were done using a series of reactors according to a planned experimental program. The results show that (i) the mean maximum temperature of the first and second stage were 65°C and 56°C of passive, 67°C and 60°C of forced aeration, respectively which raised within seven days. (ii) According to the mass balance, total mass, moisture content, and volatile solids always decreased at every stage for passive and forced aeration processes, the degradation of the volatile solid in the composting process using forced aeration was more than in the passive aeration process. (iii) For the passive and forced aeration processes, the total BVS degradation of ranged between 82% and 89%, and 73% and 91%, respectively after 60 days. Therefore, it can be concluded that the percentage of BVS degradation in forced and passive aeration was not significantly different.Implications: The extent of degradation was determined through different composting processes in the three stages with different mixture proportion of fecal sludge and organic solid waste. The study showed that maximum temperature in composting ranged from 57°C to 67°C within one week. Co-composting process with passively and forced aeration process of peak temperature were almost same. Reduction of volatile solids at first stage was greater than second and third stages. Biodegradable volatile solids reduction in passive and forced aeration processes were not significantly different. The final product of composting was used in agricultural land.

Study on dynamic changes of microbial community and lignocellulose transformation mechanism during green waste composting

There are few reports on the material transformation and dominant microorganisms in the process of greening waste (GW) composting. In this study, the target microbial community succession and material transformation were studied in GW composting by using MiSeq sequencing and PICRUSt tools. The results showed that the composting process could be divided into four phases. Each phase of the composting appeared in turn and was unable to jump. In the calefactive phase, microorganisms decompose small molecular organics such as FA to accelerate the arrival of the thermophilic phase. In the thermophilic phase, thermophilic microorganisms decompose HA and lignocellulose to produce FA. While in the cooling phase, microorganisms degrade HA and FA for growth and reproduction. In the maturation phase, microorganisms synthesize humus using FA, amino acid and lignin nuclei as precursors. In the four phases of the composting, different representative genera of bacteria and fungi were detected. Streptomyces, Myceliophthora and Aspergillus, maintained high abundance in all phases of the compost. Correlation analysis indicated that bacteria, actinomycetes and fungi had synergistic effect on the degradation of lignocellulose. Therefore, it can accelerate the compost process by maintaining the thermophilic phase and adding a certain amount of FA in the maturation phase.

Identification of a thermophilic protease-producing strain and its application in solid-state fermentation of soybean meal

BACKGROUND

Thermophiles can thrive at 50-80 °C and produce some enzymes with special promise for biocatalysis. A thermophilic protease-producing strain YYC4 was isolated from Yunyan cigarette and employed in solid-state fermentation (SSF) of unsterilized soybean meal (SBM).

RESULTS

The isolate was identified as Bacillus licheniformis based on appearance of colonies, microscopic observation and 16S rDNA sequencing. After SSF, soluble and crude protein contents in SBM increased from 49.24 to 185.73 g kg-1 and from 404.18 to 479.46 g kg-1 , respectively, under the fermentation conditions of 107  cfu g-1 inoculation of strain YYC4, 1:1.8 (g mL-1 ) SBM to distilled water, 1.2 g kg-1 magnesium sulphate addition, 55 °C and 48 h. During fermentation, pH of the medium increased from 6.30 to 9.09 and protease activity especially neutral protease increased significantly from 13.5 to 181.31 U g-1 . Meanwhile, trypsin inhibitor (TI) activity was decreased from 8.19 to 3.19 mg g-1 . The safety of fermented SBM (FSBM) was verified by acute toxicity animal experiment. Analysis of microbial community in FSBM showed that Bacillus licheniformis YYC4 as a dominant strain inhibited most of the other microorganisms pre-existing in the materials during fermentation.

CONCLUSION

Increments of soluble and crude protein by 277.19% and 18.63% and decrement of harmful TI by 61.05% in SBM were achieved using thermophilic SSF by Bacillus licheniformis YYC4, providing a basis for the application of thermophiles in fermentation industry in an environmentally friendly and energy-saving way. © 2021 Society of Chemical Industry.

Fallen leaves are superior to tree pruning as bulking agents in aerobic composting disposing kitchen waste

Though aerobic composting has been frequently applied to kitchen waste disposal, appropriate bulking agents are essential to acquire a promising performance. Fallen leaves and tree pruning in urbans face huge disposal demands and have great potentials as bulking agents of aerobic composting while have been seldom examined yet. This study comparably explored the performance of fallen leaves bulked and tree pruning bulked aerobic composting disposing kitchen waste. Results indicated that though both reactors were effective in degrading kitchen waste, leaf bulked composting was superior to tree pruning bulked composting in terms of longer thermophilic period and higher maximum temperature, higher organics degradation efficiency, higher humification and less odorous gas emission. Bacterial community was a driving mechanism for above results. This study shows that fallen leaves bulked aerobic composting has great potentials for kitchen waste disposal.

Influence of microbial inoculants on co-composting of lignocellulosic crop residues with farm animal manure: A review

The rapidly developing agro-industry generates huge amounts of lignocellulosic crop residues and animal manure worldwide. Although co-composting represents a promising and cost-effective method to treat various agricultural wastes simultaneously, poor composting efficiency prolongs total completion time and deteriorates the quality of the final product. However, supplementation of the feedstock with beneficial microorganisms can mitigate these negative effects by facilitating the decomposition of recalcitrant materials, enhancing microbial enzyme activity, and promoting maturation and humus formation during the composting process. Nevertheless, the influence of microbial inoculation may vary greatly depending on certain factors, such as start-up parameters, structure of the feedstock, time of inoculation, and composition of the microbial cultures used. The purpose of this contribution is to review recent developments in co-composting procedures involving different lignocellulosic crop residues and farm animal manure combined with microbial inoculation strategies. To evaluate the effectiveness of microbial additives, the results reported in a large number of peer-reviewed articles were compared in terms of composting process parameters (i.e., temperature, microbial activity, total organic carbon and nitrogen contents, decomposition rate of lignocellulose fractions, etc.) and compost characteristics (humification, C/N ratio, macronutrient content, and germination index). Most studies confirmed that the use of microbial amendments in the co-composting process is an efficient way to facilitate biodegradation and improve the sustainable management of agricultural wastes. Overall, this review paper provides insights into various inoculation techniques, identifies the limitations and current challenges of co-composting, especially with microbial inoculation, and recommends areas for further research in this field.

Adding an appropriate proportion of phosphogypsum ensured rice husk and urea composting to promote the compost as substrate utilization

To explore the effectiveness of urea replacing poultry manure as the nitrogen source in the rice husk composting system, and to promote the utilization of compost products as substrates, 0%, 10%, 20%, and 30% of phosphogypsum were added respectively in the urea composting system, and were compared with the chicken manure composting (RCP0). Finally, the fermentation and maturation of RCP0 were achieved, but high EC value limited the utilization of compost products as the substrate. Urea, as an N source, could lower the EC value, but the C/N ratio was uncoordinated during the initial stage of composting. Adding an appropriate proportion of phosphogypsum could ensure a proper C/N ratio to promote smooth fermentation and enable the products to be ideal substrates. When the added proportion was 30%, the thermophilic stage was shortened significantly but this may increase heavy metals. 10%-20% were concluded to be the recommended proportion.

Fungal pretreatment facilitates the rapid and valuable composting of waste cardboard

This study investigates the waste cardboard (WCB) fungal pretreatment (Oligoporus placenta and Tremetes hirsuta) under monoculture and mixed culture and then composting for 35 d after mixing with cow dung in different ratios. Fungal pretreatment caused significant reduction in cellulose (28.3-35.8%), hemicellulose (61.4-68.4%), lignin (67.5-69.3%) content in WCB. Pretreated WCB showed better rates of decrement in total organic carbon (26.02-47.92%), carbon-to-nitrogen ratio (19.4-23.5), and lignocellulose contents, as well as incensement in total nitrogen (40.48-63.31%), total potassium (51.92-73.91%), germination index (88.5-102.0%), and elemental (Cu, Fe, Zn, Cr, and Mn) levels. Dehydrogenases (142-210 µg g^-1h^-1), and β-galactosidase (210-256 µg g^-1h^-1) activities indicates high microbial-mediated mineralization in setups. Results suggested that WCB could be used as a valuable substrate for valuable-added compost preparation after pretreating with a consortium of white-rot fungi.

Impact of Soil Microbes and Oxygen Availability on Bacterial Community Structure of Decomposing Poultry Carcasses

The impact of soil with an intact microbial community and oxygen availability on moisture content, soil pH, and bacterial communities during decomposition of poultry carcasses was investigated. Poultry carcasses were decomposed in soil with or without a microbial community, under aerobic or anaerobic conditions. The samples collected in each microcosm burial set-up were analyzed by targeted 16S rRNA amplicon sequencing and Amplicon sequence variants (ASV) method. Our results showed that moisture was high in the burial set-ups under anaerobic conditions and pH was high in the burial set-ups under aerobic conditions. Meanwhile, the Chao1 and Shannon index significantly differed between the different burial set-ups and across different time points. In addition, bacterial taxa composition during the early period of decomposition differed from that of the late period. A total of 23 phyla, 901 genera, and 1992 species were identified. Firmicutes was the most dominant phyla in all burial set-ups throughout the decomposition. At day 60, Pseudogracilibacillus was dominant in the burial set-ups under aerobic conditions, while Lentibacillus dominated in the burial set-ups under anaerobic conditions. This study demonstrated that the soil microbial community and availability of oxygen significantly affected the changes in moisture content, pH, and bacterial composition during the decomposition process.

Identification and characterisation of a novel heptapeptide mackerel by-product hydrolysate, and its potential as a functional fertiliser component

Functional fertilisers for hydroponics are in great demand. Herein, we isolated peptides from mackerel by-products, a valuable source of bioactive peptides. The pellet-phase fraction obtained after cold-acetone extraction exhibited plant growth-promoting activity in wheat hydroponics, and the presumed peptides were determined to be ≤ 1 kDa based on molecular weight cut-off and tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Size exclusion chromatography and matrix-assisted laser desorption ionisation time of flight mass spectrometry analysis were employed for peptide purification and identification. Finally, two peptides were identified, both with linear structures, consisting of amino acid sequences TCGGQGR and KEAGAFIDR. At 1 mg/mL, the heptapeptide performed better than the nonapeptide in terms of wheat growth and health, but neither peptide exhibited antimicrobial activity. Only the heptapeptide displayed significant antioxidant activity, and this activity bioaccumulated in wheat leaves after 7 days of hydroponic growth. The heptapeptide did not match any known metabolites in PepBank, BIOPEP, UniProt or METLIN databases, and is therefore a novel peptide with potential as a functional fertiliser component.

Effects of different additives on the chemical composition and microbial diversity during composting of Camellia oleifera shell

The influence of three additives including Camellia oleifera meal, C. oleifera seed cake and goat dung during the C. oleifera shell composting was evaluated. The result of physic-chemical parameters indicated that compost of C. oleifera shell with one of additives could achieve the effect of maturity.16S rDNA sequencing suggested that Proteobacteria, Bacteroidetes, Firmicutes, Actinobacteria, Chloroflexi, Tenericutes, Deinococcus-Thermus, Patescibacteria, Fibrobacteres and Acidobacteria were the dominant microorganisms in all compost piles, and their abundances varied with compost additive and composting phase. Goat dung significantly increased the microbial diversity at the mesophilic phase. The microbial composition was most diverse at the end of composting for all piles. No pathogens were detected in the compost products of all three groups, and thus were safe for utilization in plant cultivation. This work considered that compost was best way to address the contamination problem of C. oleifera shell, where goat dung was best additive for compost.

Development of a compound microbial agent beneficial to the composting of Chinese medicinal herbal residues

This study was aimed at developing a compound microbial agent to facilitate the composting of Chinese medicinal herbal residues (CMHRs). Different microbial agents were inoculated into a mixture of CMHRs, sheep manure, and biochar and composted for 42 days. The results demonstrated that the compound microbial agent (K1 + P1 + N4) inoculated in T1 can extend the thermophilic period during composting. Compared with control check (CK), the total nutrient contents of the vaccinated groups increased by 5.45-28.54%, and T1 had the highest value. The total organic carbon degradation rate and germination index of T1 were 1.95 and 1.03 times higher than those of the control. Moreover, significant increases in the abundance and diversity of the microbial community were also found in T1. Consequently, using K1 + P1 + N4 as a microbial agent for the composting of CMHRs is recommended, and this research provides a new idea to solve the problem of waste of CMHRs.

Maturity and stability assessment of composted tomato residues and chicken manure using a rotary drum bioreactor

The efficiency of the composting process for tomato residues and chicken manure was estimated after monitoring of the rotary composting system. Physicochemical parameters and Compost Quality Index were evaluated. The tomato residues (leaves, stems, and some green and damaged fruits) were collected, cut into small pieces, moistened approximately (60-65%), and mixed with 20% chicken manure then distributed into three rotary drum bioreactors. The obtained results showed that, the temperature above 50°C was maintained for more than two days. Carbon: nitrogen (C:N) ratio was reduced from 30:1 to 19.13:1. The pH value ranged between 7 and 8.80 during the composting process, while the electrical conductivity (EC) ranged between 2.67 to 4.53 dS/m. Both compost quality parameters (Dewar and germination index) and (Solvita-CO₂ and Solvita-NH₃) indicated that, the final compost is stable and mature.Implications: The idea of this research revolves around assessing the maturity and stability of the compost resulting from mixing tomato residues with chicken manure, using a rotary drum bioreactor which is characterized by reducing the time of the active phase to several hours or days instead of weeks or months. Several tests related to the maturity and stability of mixture have been used to judge its quality. Also, many parameters related to this topic were monitored and discussed with many previous researches to determine the importance of benefiting from mixing the different wastes together and obtaining a good fertilizer ready for application as an agricultural substrate or a soil conditioner.

Feasibility of vermicomposting for spent drilling fluid from a nature-gas industry employing earthworms Eisenia fetida

This study investigated the vermicomposting of spent drilling fluid (SDF) from the nature-gas industry mixed with cow dung in 0% (T1), 20% (T2), 30% (T3), 40% (T4), 50% (T5), and 60% (T6) ratio employing Eisenia fetida under a 6 weeks trial. Eisenia. fetida showed better growth and reproduction performances in the first three vermireactors (T1-T3), and the mortality was higher in the vermireactors that contained more spent drilling fluid (≥40%). Vermicomposting results in a decrease in total organic carbon, C/N ratio, and an increase in EC, total nitrogen, total phosphorous, total potassium compared to their initial values. The RadViz and VizRank showed that vermicomposting results in a greater impact on the C/N ratio (15.24-35.48%) and EC (7.29-26.45%) compared to other parameters. Activities of urease and alkaline phosphatase during vermicomposting initially increased and then declined suggesting vermicompost maturity. Also, seed germination, mitotic index and chromosomal abnormality assays using cowpea signified that the vermicomposts T2 is suitable for agricultural use due to the lower phytotoxicity and cytotoxicity. The results indicated that SDF could be converted into good quality manure by vermicomposting if mixed up to 20% with cow dung.

Full-Scale Composting of Different Mixtures with Meal from Dead Pigs: Process Monitoring, Compost Quality and Toxicity

ABSTRACT

Abundant by-products of large swine industries, such as slaughterhouse sludge and carcasses, require adequate treatment to prevent negative effects of their direct disposal in the open environment. This study is aimed to evaluate the efficiency of composting using meal from dead pigs through physicochemical analyses and phytotoxic assays. Five treatments were tested, all including 50% sawdust: T1, with 50% slaughterhouse sludge (control); T2, with 20% slaughterhouse sludge and 30% meal from dead pigs; T3, with 10% slaughterhouse sludge and 40% meal from dead pigs; T4, with 20% organic stabilizing compost and 30% meal from dead pigs and T5, with 30% organic stabilizing compost and 20% meal from dead pigs. The phytotoxicity assays used lettuce, cucumber, celia, soybean, rice and wheat as bioindicators. Inclusion of meal from dead pigs was related to reduction in pH, C/N ratio, humidity and temperatures inside the pile, although thermophilic peaks lasted longer than 50 days and the final composts showed high content of nitrogen and phosphorous. The germination of bioindicators was reduced in all tested treatments, compared to the control. The composts from treatments that included meal from dead pigs presented acceptable nutrient content, which may indicate their use as organic fertilizers. However, after 4 months, all bioindicators in contact with such composts presented impaired germination.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12649-021-01422-0.

Cellulase Interacts with Lactic Acid Bacteria to Affect Fermentation Quality, Microbial Community, and Ruminal Degradability in Mixed Silage of Soybean Residue and Corn Stover

The objective of this experiment was to investigate the effect of lactic acid bacteria (LAB) and cellulase (CE) on the fermentation quality, rumen degradation rate and bacterial community of mixed silage of soybean residue (SR) and corn stover (CS). The experiment adopted a single-factor experimental design. Four treatment groups were set up: the control group (CON), lactic acid bacteria treatment group (LAB), cellulase treatment group (CE) and lactic acid bacteria + cellulase treatment group (LAB + CE). Among them, the amount of added LAB was 1 × 10⁶ CFU/g, and the amount of added CE was 100 U/g. After 56 days of mixed silage, samples were taken and analyzed, and the chemical composition, fermentation quality, rumen degradation rate and microbial diversity were determined. The results showed that the pH of each treatment group was significantly (p < 0.05) lower than that of CON, while the lactic acid and ammoniacal nitrogen contents of each treatment group were significantly higher than that of CON, with the highest contents in the LAB + CE group. The contents of DNFom (Ash-free NDF), ADFom (Ash-free ADF) and DM in the LAB + CE group were significantly lower than those in the CON group, while the content of crude protein (CP) was significantly higher than that in the CON group. The in situ effective degradation rates of DM (ISDMD), DNF (ISNDFD) and CP (ISCPD) were all significantly (p < 0.05) higher in each treatment group than in the control group. The results of principal component analysis showed that the bacterial composition of the LAB, CE and LAB + CE groups was significantly different from that of the CON group (p < 0.05). Bacterial genus level analysis showed that the content of lactic acid bacteria was significantly higher in the LAB + CE group than in the other treatment groups (p < 0.05), while the content of undesirable bacteria was significantly lower than in the other treatment groups. The results showed that the addition of Lactobacillus and/or cellulase in mixed silage of SR and CS could effectively improve the quality of mixed silage fermentation, rumen degradation rate and microbial diversity, with better results when Lactobacillus and cellulase were added together, which provides new ideas for better application of SR and CS in dairy production.

Production of compost with biopesticide property from toxic weed Lantana: Quantification of alkaloids in compost and bacterial pathogen suppression

Toxic weed Lantana camara foliage was composted with cow dung in 2:1 and 1:1 ratio (v/v) and changes in physicochemical characteristics, and faecal coliform bacterial population (Escherichia coli and Salmonella) was estimated for 35 d. Results showed a significant increase in total N (1.48-1.69-folds), Paval (6.87-9.19-folds), and total K (1.08-1.23-folds) content, while a decrease in C/N ratio (1.87-2.13-folds) and total organic carbon (1.12-1.46-folds) after composting process. Germination index (GI) results (> 70 %) suggested the non-toxic property of Lantana compost against tested rapeseed mustard seeds. E. coli and Salmonella population reduced to the safe limit after 35 d composting. Compost extract (sterilized and non-sterilized) (from 2:1 setup) showed about 0.88 - 1.08-, 0.88 - 0.96-, 0.83 - 0.94-, and 0.79-1.08-folds higher inhibition in Xanthomonas citrus, Xanthomonas campestris, Erwinia carotovora, and Pseudomonas aerogenosa, respectively, indicating strong pathogen-inhibiting substances in Lantanacompost. GC-MS analysis of compost extract indicated the presence of isomers of several compounds of biocidal property - hexadecane (9-hexyl and 9-octyl); 2-tridecyl ester; eicosane; tetradecane, heptacosane (1-chloro- and 9-hexyl); heptadecane, octadecane, 3-ethyl-5-(2-ethylbutyl)-, heptacosane, tetradecane, 2,6,10-trimethyl-, etc.). Result revealed that Lantana compost could be used as biomanure with biopesticide properties for sustainable organic farming system.

Vermicomposting of livestock manure as affected by carbon-rich additives (straw, biochar and nanocarbon): A comprehensive evaluation of earthworm performance, microbial activities, metabolic functions and vermicompost quality

Vermicomposting is an eco-friendly method for treating organic wastes. This study investigated the effects of the addition of straw (S), biochar (B), nanocarbon (N), S + B and S + N to cow dung (CD) on earthworm (Eisenia fetida) performance, microbial properties and vermicompost quality. In general, the earthworm growth rate and cocoon production were enhanced by straw addition, but were inhibited by biochar or nanocarbon addition. However, biochar and nanocarbon increased microbial communities associated with organic matter decomposition, and improved metabolic functions, enzyme activities and vermicompost properties. Moreover, addition of straw in combination with nanocarbon resulted in the highest vermicompost quality index (VQI), and significantly increased the biomass of three different test crops (radish, lettuce and pakchoi). These results indicated that biochar and nanocarbon mainly improved microbial activities, while straw primarily enhanced earthworm performance during vermicomposting. In addition, straw combined with nanocarbon can be used to enhance the agronomic performance of vermicompost.

Fate of faecal pathogen indicators during faecal sludge composting with different bulking agents in tropical climate

In recent years, composting has increasingly been promoted as a reliable method for sanitizing Faecal Sludge (FS) from onsite sanitation systems, particularly where there are opportunities to use the recovered nutrients in agriculture. However, there remain gaps in our understanding of the fate of infectious faecal pathogens during composting, particularly in tropical climates. This study investigated the influence of different locally available bulking agents on the inactivation efficiency of composting by tracking the fate of four key indicator organisms (E. coli, Salmonella spp., Enterococci spp., and viable helminth eggs). Dewatered FS was mixed with different bulking agents - i.e. Sawdust (SD), Coffee husks (CH) and Brewery waste (BW). Compost piles of FS:SD, FS:CH, and FS:BW in a volumetric ratio of 1:2 were set-up in duplicate (3 m³ each), composted on a pilot scale and monitored weekly for the survival of pathogen indicators for a period of 15 weeks. The study findings suggest that the different bulking agents have a statistically significant (p < 0.05) effect on the temperature evolution and survival of pathogen indicators in compost. CH was the most suitable bulking agent for composting with FS as piles containing CH exhibited higher pathogen inactivation efficiency and shorter inactivation periods of 6 weeks compared to 8 weeks for SD and BW piles. Time-temperature was the most important factor responsible for pathogen inactivation. However, other mechanisms such as indigenous microbial and toxic by-products such as NH₄₊-N also played an important role in the inactivation of pathogens. The results suggest that co-composting of FS with a sawdust, coffee husk or brewery waste for 8 weeks with thermophilic temperatures of about 48-60 °C sustained in the composting piles for more than 38 days, using 7 days turning frequency, is sufficient to ensure complete sanitization of FS before reuse in agriculture.

Synergistic effects of compost, cow bile and bacterial culture on bioremediation of hydrocarbon-contaminated drill mud waste

Bioremediation has gained global prominence as an effective method for treating hydrocarbon-contaminated drill mud waste (HCDW). However, the problem of low nutrient content, bioavailability and microbial presence remain largely unresolved. In this study, the synergistic effects of compost, cow bile and bacterial culture on the degradation rate of HCDW was investigated. A homogenized HCDW sample (80 kg) obtained from 25 different drill mud tanks was divided into 20 portions (4 kg each) and each adjusted to 1.4% nitrogen content + 20 ml cow bile (i.e., basic treatment). Pure cultures of Brevibacterium casei (Bc) and Bacillus zhangzhouensi (Bz) and their mixture (BcBz) were subsequently added to 12 of the amended HCDW (basic) to undergo a 6-week incubation. A portion of the unamended HCDW (2 kg) was used as control. Initial pH, electrical conductivity and surface tension values of the HCDW were 8.83, 2.34 mS/cm and 36.5 mN/m, respectively. Corresponding values for total petroleum hydrocarbon (TPH), total nitrogen and total plate count bacteria were 165 g/kg, 0.04% and 4.4 × 10² cfu/ml. The treatments led to a substantial reduction in TPH (p < 0.05) while the control had no significant effect (p > 0.05). TPH reduction after the experimental period occurred in the order: basic + BcBz (99.7%) > basic + Bz (99.5%) > basic + Bc (99.2%) > basic (95.2%) > control (0.06%). Multiple regression analysis revealed significant effect of total plate count, pH, CN ratio and electrical conductivity (R² = 0.87, p = 0.05) on the degradation of TPH in the HCDW. The study demonstrates strong interactive effects of compost, cow bile and bacteria culture on the remediation of HCDW, which can be applied to boost the efficiency of the bioremediation technique.

Biochar combined with gypsum reduces both nitrogen and carbon losses during agricultural waste composting and enhances overall compost quality by regulating microbial activities and functions

Composting is an efficient method for treating agricultural wastes. This study investigated the effects of the addition of biochar (B) and gypsum (G) to straw mixed with chicken manure (SC) (i.e. SC, SC + B, SC + G and SC + B + G) on composting performance at different initial C/N ratios (20, 25 and 30). In general, biochar combined with gypsum (BCG) efficiently shortened composting time and reduced N loss, C loss and potential ecological risk. It also enhanced lignocellulose decomposition, nutrient retention and the overall compost quality expressed by a compost quality index (CQI), and increased the biomass of four different test crops. The BCG-induced increase in CQI was closely associated with microbial enzyme activities and C catabolic profiles. These results indicated that the combination of biochar and gypsum is more effective than each single additive during composting, and emphasized that microbial activities and functions play pivotal roles in determining compost quality and thereby agronomic performance.

Trichoderma strains accelerate maturation and increase available phosphorus during vermicomposting enriched with rock phosphate

AIMS

To suggest microbial inoculation as a tool to shorten organic residues stabilization and increase rock phosphate (RP) solubilization through vermicomposting, thus increasing nutrient content in plants and making it more appealing to farmers. Two Trichoderma strains were inoculated alone or combined in a RP apatite-enriched vermicompost. Stability and plant-available phosphorus levels were monitored for 120 days.

METHODS AND RESULTS

Observable higher total organic carbon reduction in the treatment with the combined Trichoderma strains, followed by the inoculation with T. asperellum and T. virens. Combined Trichoderma and inoculation with T. virens increased humic acids (HA) content in 38·2 and 25·0%, respectively; non-inoculated vermicompost with T. asperellum increased it by 15·0%. The combined Trichoderma strains and T. virens achieved the stability index based on the humic/fulvic acids (HA/FA) ratio after 120 days. T. asperellum, combined Trichoderma and T. virens increased the citric acid soluble-P content in 83·2, 62·2 and 49·5%, respectively, compared to the non-inoculated vermicompost.

CONCLUSIONS

Inoculation with combined T. asperellum and T. virens efficiently accelerated vermicompost stabilization; T. asperellum increased the citric acid soluble-P in the final product.

SIGNIFICANCE AND IMPACT OF THE STUDY

Combined Trichoderma inoculation and RP enrichment improves the vermicompost quality, increasing HA and citric acid soluble-P, recycling organic waste nutrients and reducing agricultural dependence on phosphate fertilizers.

Effects of carbon-based additives and ventilation rate on nitrogen loss and microbial community during chicken manure composting

Aerobic composting is a sustainable method for chicken manure recycling, while its unsuitable porosity and carbon to nitrogen ratio (C/N) may result in high nitrogen loss and incomplete composting. With the aim to investigate the effects of carbon-based additives and two ventilation rates on chicken manure composting and microbial community, two series of treatments were set up for chicken manure composting, in order to investigate their effects on the biodegradation process, ammonia (NH₃) emission, nitrogen loss, physiochemical properties and microbial community. The results showed that additives and ventilation rates set in the current study influenced the carbon dioxide (CO₂) production from the 2^nd week and also the physiochemical parameters during the entire process, while no inhibitory effect on the maturity were observed. With woody peat as additive, the NH₃ emission amount and nitrogen loss rate were shown as 15.86 mg and 4.02%, less than those in other treatments, 31.08–80.13 mg and 24.26–34.24%, respectively. The high aeration rate increased the NH₃ emission and nitrogen loss, which were varied when the additives were different. The terminal restriction fragment length polymorphism (T-RFLP) results showed that the additives and the ventilation rates changed the microbial community, while the prominent microbial clones belonged to the class of Bacilli and Clostridia (in the phylum of Firmicutes), and Alphaproteobacteria, Deltaproteobacteria and Gammaproteobacteria (in the phylum of Proteobacteria). Bacillus spp. was observed to be the most dominant bacteria in all the composting stages and treatments. It was concluded that woody peat could improve chicken manure composting more than other additives, especially on reducing nitrogen loss, meanwhile 0.18 L‧min^-1‧kg^-1 DM was suitable for various additives. Therefore, suitable additive and aeration rate could be used in practical application, which could significantly reduce nitrogen loss without influence on the compos maturity process.

Composting of toxic weed Parthenium hysterophorus: Nutrient changes, the fate of faecal coliforms, and biopesticide property assessment

This study aimed to investigate; composting of toxic weed Parthenium with cow dung in (2:1, and 1:1 ratio); and the changes in Escherichia coli and Salmonella population; as well as the antimicrobial property of ready compost. Organic carbon decreased by 45-52% while total nitrogen, total potassium, available phosphorus increased by 1.87- to 3.21-, 1.65- to 1.83-, and 4.03- to 3.33-folds, respectively in Parthenium setups. Germination index value (110-132%) indicates no phytotoxicity of composted Parthenium. E. coli reduced by 6.87 to 6.90 log population (<1000 CFU g^-1, safe limit) while Salmonella was in non-detectable limit in compost samples. Results of the antimicrobial test indicate a strong biocidal activity by non-sterilized compost extract against plant pathogens Xanthomonas citrus, Xanthomonas campestris, and Erwinia carotovora. Xanthomonas spp. It is concluded that thermophilic composting could convert Parthenium into a product with biomanure and biopesticide property for sustainable agriculture production.

Vermicomposting of invasive weed Ageratum conyzoids: Assessment of nutrient mineralization, enzymatic activities, and microbial properties

Ageratum conyzoids biomass was vermicomposted with cow dung in 25 (T₂₅), 50 (T₅₀), and 75 (T₇₅) % (v/v) ratios and changes in physicochemical characteristics, enzymatic activities (proteases, dehydrogenases, β-galactosidase and phosphatases), and microbial population (bacterial, fungal, and actinomycetes) was recorded. Vermicomposting caused a decrease in pH, OC_total (27.3-35.3%), but an increase in N_total (59.6-69.9%), P_aval (53.8-148.7%), K_total (32.2-92.43%), and Ca_total (25.5-55.3%). The peaked enzymatic activities were recorded between 5 and 15 d. T₅₀ and T₇₅ showed the highest fold increase in bacteria (2.09-to-2.51), fungi (1.48-to-2.41), actinomycetes (1.52-to-1.79) population. The maximum biomass (883.67-1480 mg), cocoon production (85.33-145.33), and population build-up in earthworm were recorded in setups with a high content of Ageratum. Germination index (>80%) and soil respiration rate suggested the non-toxic impact of vermicomposted Ageratum. Results indicate that Ageratum could be biotransformed into toxic-free manure through vermitechnology.

Vermicomposting of duckweed (Spirodela polyrhiza) by employing Eisenia fetida: Changes in nutrient contents, microbial enzyme activities and earthworm biodynamics

This study investigated the vermicomposting of duckweed (DW) mixed with cow dung in 25 (T₂₅), 50 (T₅₀), 75 (T₇₅), 100% (T₁₀₀) ratio using Eisenia fetida under a 35 d trail. Decrease in pH, organic carbon (33.54-38.25%), C/N ratio (43.6-56.6%), but increase in total N (18.2-42.4%), P_aval (137-187%), and TK (7.76-79.4%) was recorded. Macro-elements (Mg, Fe, Zn, Mn, and Cu) also showed a many-fold increase in vermicomposts. T₅₀ and T₇₅ showed the highest mineralization rates. Activities of enzymes (proteases; dehydrogenases; β-galactosidase; acid phosphatase; and alkali phosphatases) and soil respiration rate was also higher in DW-rich waste mixtures. Seed bioassay test indicates the high agronomic application of DW-based vermicomposts. High earthworm biomass (975-1395 mg) and fecundity rate (1.53-4.07 cocoons worm^-1) was recorded in all vermi-setups suggesting the suitability of DW as a substrate for E. fetida culture.

Malek R. Inventory and composting of yard waste in Serdang, Selangor, Malaysia

Composting of yard waste is one of the waste management approaches in the Malaysian Agricultural Research and Development Institute (MARDI) in Serdang, Selangor, Malaysia. The yard waste inventory was developed in the headquarters' area and a pilot-scale study was performed on the potential compost product. The total amount of yard waste generated from June 2017 to December 2017 was 16.75 tonnes with an average generation of 0.60 tonnes per week on the dry weight (d.w.) basis. The collected yard waste consisted of three major characteristics, namely dry leaves, fresh green leaves, and grass cuttings, and a waste estimation technique was applied to determine the composition of these three elements. The acquired information was used to formulate the initial compost mixture. The wastes were then mixed with an appropriate amount of livestock manure and other wastes to obtain the optimum initial C/N ratio, which was then found in the analysis to range between 25:1 and 42:1. Meanwhile, the C/N ratios obtained from the matured compost product were from 10:1 and 15:1. Moreover, most of the compost yield ranged between 50% and 70% (w w-1 d.w. basis), while the percentage of the seed germination in the compost was over 95%. The viability of the project was indicated from the economic analysis, with benefit to cost ratio (BCR) values of more than 1. The results also suggested that the large scale composting of yard waste in MARDI was feasible and its applicability is continuous. This technique also fulfilled the objective of producing quality compost, which was suitable for agricultural use.

Effect of bean dregs amendment on the organic matter degradation, humification, maturity and stability of pig manure composting

The purpose of this study was to effectively dispose of bean dregs (BD) using composting technology, which could provide a theoretical basis for the disposal of BD. Therefore, the influence of different quantities of bean dregs (BD) (0%, 5%, 10% and 15%, w/w with a dry base of pig manure (PM)) on the decomposition and humification of organic matter during PM-composting was investigated, and a 0% BD amendment was used as the control (CK). Wheat straw was used as a bulking agent. Compared to the CK, the BD amendment promoted the degradation of organic matter. The degree of organic matter degradation increased by 16.46-25.04% upon BD amendment. Furthermore, the BD amendment improved humification and increased indices of the humification ratio (HR), percentage of humic acids (PHA), degree of polymerization (DP) and the humification index (HI). Furthermore, Fourier transform infrared (FTIR) spectroscopy indicated that the aromatic structure was enhanced with the BD amendment, and excitation-emission matrix (EEM) fluorescence spectra showed increased humic-like substance production. Additionally, the dissolved organic carbon (DOC), germination index (GI), electrical conductivity (Ec) and carbon/nitrogen (C/N) influenced the maturity and stability of composting. Comparatively, a 10% BD addition showed the optimal performance among all PM-composting treatments.

Enzymatic activities triggered by the succession of microbiota steered fiber degradation and humification during co-composting of chicken manure and rice husk

The carbon to nitrogen ratio (C/N) is well known for its importance in the composting process, however the fiber degradation and humification associated with enzymatic activity and microbial variation derived from different C/N ratios are poorly studied. Here, we designed two treatments of chicken manure with 15% (initial C/N ratio 9.61) and 50% (initial C/N ratio 17.3) rice husk to adjust the moisture of mixtures for turning feasibly by towable fertilizer turner in industrial level. Compared to the C/N ratio 9.61, the suitable C/N ratio of 17.3 significantly enhanced the composting efficiency and the final germination index (23.7%). Moreover, the suitable C/N ratio increased the relative abundance of Bacilli, which played an important role during the mesophilic and thermophilic phases. Bacilli abundance was related to cellulose and β-glycosidase activities, thus improved fiber degradation and humification. This study not only seeks a swift method in industrial level to process chicken manure but also provides insight into the enzymatic activity of microbial community related to high-efficient composting.

RETRACTED: Increased abundance of nitrogen fixing bacteria by higher C/N ratio reduces the total losses of N and C in cattle manure and corn stover mix composting

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief. The article duplicates significant parts of a paper that had already appeared in Bioresource Technology, Volume 297, February 2020, 122410, https://doi.org/10.1016/j.biortech.2019.122410. One of the conditions of submission of a paper for publication is that authors declare explicitly that the paper has not been previously published and is not under consideration for publication elsewhere. Re-use of any data should be appropriately cited. As such this article represents a misuse of the scientific publishing system. The scientific community takes a very strong view on this matter and apologies are offered to readers of the journal that this was not detected during the submission process.

Increased abundance of nitrogen transforming bacteria by higher C/N ratio reduces the total losses of N and C in chicken manure and corn stover mix composting

The aim of this work was to investigate how the initial C/N ratio during composting of chicken manure/corn stover mix affected the succession of dominant bacteria in the mix which led to the reduction of the total losses of N and C in the composting process. 16S rDNA sequencing indicated that the succession of predominant bacteria was significantly affected by the temperature and the initial C/N ratio during composting. Redundancy analysis showed that higher C/N appeared to promote the relative abundance of nitrogen fixing bacteria Thermoactinomyces, Planifilum, Flavobacterium, Bacillaceae, Pseudomonas,Sphingobacterium, Paenibacillus, Bacillus and Thermobifida, while compressing the denitrifying bacteria Pusillimonas, Ignatzschineria, Alcanivorax, Cerasibacillus, Truepera and Erysipelothrix. C/N ratio of 30:1 yielded the least C/N losses in the composting process, indicating that adjustment to the initial C/N ratio could affect nitrogen transforming bacteria to reduce the total losses of N and C and improve compost quality.

Improving municipal solid waste compost process by cycle time reduction through inoculation of Aspergillus niger

A lack of understanding about the effect of microorganism inoculation on compost production and relatively expensive downstream processing are the main obstacles towards an economic compost production. Our work tries to fill this gap. For this, influence of inoculation on the composting of organic fraction of municipal solid waste (OFMSW) to produce compost with higher agronomic value was evaluated. Three similar aerated bioreactors (A, B and C) with the same size and shape in laboratory scale designed. Reactor A was inoculated with the Aspergillus niger IBRC-M 30095, reactor B was inoculated with old compost and reactor C was used as a control. During the composting process temperature, moisture, pH, and electrical conductivity (EC) were evaluated. Also, the ratio of carbon to nitrogen (C/N) and germination index (GI) were measured in during process to evaluate compost maturity. The results of this study showed that the C/Ns decreased to about 63.37%, 59.6% and 46% for bioreactors B, A and control, respectively. Also maximum GI and temperature reached to about 138% and 59 °C in reactor B. Furthermore, our results showed that inoculation with this microorganism reduces process time to 18 days that is better than the results of other researchers and thus results in cost savings. However, we think, Aspergillus niger is appropriate candidate for compost production as a model. Graphical abstractSchematic diagram of experimental reactors: Reactor A was inoculated with the Aspergillus Niger IBRC-M 30095, reactor B was inoculated with old compost and reactor C used as a control without inoculation; (1) composting tank; (2) air compressor; (3) gas flow meter; (4) air regulator; (5) thermal probe; (6) exhausted gas; (7) mixer; (8) effluent; (9) moisture content probe; (10) sampling; (11) electric motor; (12) pump.

Toxicity evaluation and management of co-composting pistachio wastes combined with cattle manure and municipal sewage sludge

To manage the pistachio de-hulling waste (PW), investigated the co-composting process using a mixture of PW and cattle manure (CM) (5.5:10 dry weight) as well as PW and municipal dewatering sewage sludge (DSS) (1:10 dry weight) at the laboratory scale for 60 days. Compost toxicity was evaluated using the seed germination index (GI). The maximum temperatures in co-composting processes of PW+CM (51.9 °C) and PW+DSS (49.9 °C) were reported on the seventh day. The increase of temperature was higher in PW+CM and remained in the thermophilic phase for five days. In both reactors, the pH rates decreased, increased, and finally remained neutral. The C/N ratio decreased in both reactors, but the reduction rate was faster in the PW+DSS reactor. Sodium (Na%) and potassium (K%) contents were increased, while the concentrations of Cu, Zn, Fe, and Mn were decreased during the processes. The numbers of parasite eggs in the final composts of the reactors containing PW+CM and PW+DSS were zero and 8 Number/4gDW, respectively. The amounts of Salmonella were zero in the final products of reactors containing PW+CM and PW+DSS. The results of GI showed that the final compost of PW+CM process was not toxic for the plants, whereas the PW+DDS final compost was toxic. In conclusion, the co-compost product of the PW+CM reactor had higher quality than the PW+DSS reactor. So, it is suitable for PW management.

Current Scenario of the Tehran Municipal Solid Waste Handling Rules towards Green Technology

This study aims to study the waste management process and recycling of municipal waste in Tehran. Currently, Kahrizak is the defined landfill area which collects the waste generated from 22 districts of Tehran. The organic wastes undergo to the windrow composting method in order to manage the partial of the waste generated in the city. Samples from the compost pile generated in Kahrizak were examined to evaluate its fertilizer value to be used further by the farmers. The results show that the obtained compost does not reach the acceptable quality to be used further in agriculture, due to lack of homogeneity, aeration and presence of heavy metals. Overall, it has been concluded that, due to the improper waste segregation and management prior to sending to landfill and presence of non-organic materials such as hazardous metals and medical wastes, causes difficulties in proper waste management, implementation and producing high quality compost. Based on this study the existence of stakeholders, society, economy and proper handling rules can effectively improve the waste management system in the country and leads to the sustainable green environment.

Effects of bean dregs and crab shell powder additives on the composting of green waste

Composting is an effective and economic technology for the recycling of organic waste. In this study, bean dregs (BD) (at 0, 35, and 45%) and crab shell powder (CSP) (at 0, 15, and 25%) were evaluated as additives during the two-stage composting of green waste (GW). The GW used in this experiment mainly consisted of branch cuttings collected during the maintenance of the urban green landscape. Combined additions of BD and CSP improved composting conditions and compost quality in terms of composting temperature, specific surface area, average pore diameter, pH and EC values, carbon dioxide release, ammonia and nitrous oxide emissions, E₄/E₆ ratio, elemental composition and atomic ratios, organic matter degradation, microbial numbers, enzyme activities, compost phytotoxicity, and environmental and economic benefits. The combined addition of 35% BD and 25% CSP to the two-stage composting of GW resulted in the highest quality compost product in only 22 days.

Nitrification within composting: A review

Composting could be regarded as a process of processes because it entails a number of complex chemical and microbiological reactions and transformations. Nitrification is one of such processes that normally takes place during the curing phase. This process has been studied in detail for wastewater treatment, and it is becoming an extensively studied topic within composting. In the past, nitrate presence in compost has been clearly perceived as a maturation indicator; however, nowadays, nitrate formation is also conceived as a way of conserving nitrogen in compost. Nitrification is a process closely linked to other processes such as ammonification and the possible loss of ammonia (NH₃). Nitrification is defined as conversion of the most reduced form of nitrogen (NH₃) to its most oxidized form (i.e. nitrate) and it is performed in two steps which are carried out by two different groups of microorganisms: the ammonia-oxidizing bacteria or archaea (AOB/AOA) and the nitrite-oxidizing bacteria (NOB). The objectives of this review are: a) to gather relevant information on nitrification, which can specifically occur during composting, b) to outline ultimate findings described by the literature in order to increase the understanding and the application of nitrification within composting, and c) to outline future research direction.

Aerobic composting of distilled grain waste eluted from a Chinese spirit-making process: The effects of initial pH adjustment

Aerobic composting of distilled grain waste (DGW) at different initial pH values adjusted by CaO addition was investigated. Three pH-adjusted treatments with initial pH values of 4 (R1), 5 (R2) and 6 (R3) and a control treatment (R0) with a pH value of 3.5 were conducted simultaneously. The results showed that R0 had an unsuccessful start-up of composting. However, the pH-adjusted treatments produced remarkable results, with a relatively high initial pH being beneficial for the start-up. Within 65days of composting, the degradation of volatile solids (VS) and the physicochemical properties of R2 and R3 displayed similar tendencies, and both produced a mature end-product, while R1 exhibited a lower VS degradation rate, and some of its physicochemical properties indicated the end-product was immature. Quantitative PCR analysis of ammonia oxidizers indicated that the occurrence of nitrification during the composting of DGW could be attributed to the activity of ammonia-oxidizing bacteria.

Rare earth and precious elements in the urban sewage sludge and lake surface sediments under anthropogenic influence in the Republic of Benin

Nowadays, sewage sludge and water bodies are subjected to heavy pollution due to rapid population growth and urbanization. Heavy metal pollution represents one of the main challenges threatening our environment and the ecosystem. The present work aims to evaluate the contamination state of the sewage sludge and lake sediments in the Republic of Benin. Twenty metallic elements including 15 rare earth elements (Eu, Sb, Cs, Nd, Pr, Gd, La, Ce, Tb, Sm, Dy, Ho, Eu, Yb, and Lu) and five precious elements (Ag, Au, Pd, Pt, and Ru) were investigated using inductive plasma-mass spectrometry. Results showed broad range concentrations of the elements. Ce, La, and Nd were present in both sediments and sewage sludge at concentrations ranging 5.80-41.30 mg/kg dry matter (DM), 3.23-15.60 mg/kg DM, and 2.74-19.26 mg/kg DM, respectively. Pr, Sm, Gd, Tb, Dy, Eu, Er, Yb, Cs, Ho, and Tm concentrations were lower (0.02-5.94 mg/kg DM). Among precious elements, Ag was detected at the highest concentration in all sites (0.43-4.72 mg/kg DM), followed by Pd (0.20-0.57 mg/kg DM) and Au (0.01-0.57 mg/kg DM). Ru and Pt concentrations were < 0.20 mg/kg DM in all samples. Pollution indices and enrichment factor indicated a strong to severe enrichment of the elements, mainly Ce and precious elements in both sediments and sewage sludge. This revealed a growing anthropogenic input which was also implied by principal component analysis. The evaluation of pollution loading index (PLI) indicated a moderate to strong contamination (0.12 ≤ PLI ≤ 0.58; 37 ≤ PLI ≤ 114, respectively, for rare earth elements and precious elements), while the degree of contamination indicated a moderate polymetallic contamination for rare earth elements and significant contamination for precious elements.

Addition of seaweed and bentonite accelerates the two-stage composting of green waste

Green waste (GW) is an important recyclable resource, and composting is an effective technology for the recycling of organic solid waste, including GW. This study investigated the changes in physical and chemical characteristics during the two-stage composting of GW with or without addition of seaweed (SW, Ulva ohnoi) (at 0, 35, and 55%) and bentonite (BT) (at 0.0, 2.5%, and 4.5%). During the bio-oxidative phase, the combined addition of SW and BT improved the physicochemical conditions, increased the respiration rate and enzyme activities, and decreased ammonia and nitrous oxide emissions. The combination of SW and BT also enhanced the quality of the final compost in terms of water-holding capacity, porosity, particle-size distribution, water soluble organic carbon/organic nitrogen ratio, humification, nutrient content, and phytotoxicity. The best quality compost, which matured in only 21days, was obtained with 35% SW and 4.5% BT.

Role and multi-scale characterization of bamboo biochar during poultry manure aerobic composting

The objective of the present study was to study the changes in compost particle and its relationship with other physicochemical process during aerobic composting employing 5%, 10%, 20% or 0% biochar. Changes of physicochemical and biological parameters and gases emissions indicated that appropriate biochar addition improved both degradation rate and final degree of the organic matter and simultaneously reduced CO₂, CH₄, N₂O and NH₃ emissions. Beneficial properties like stability and high porosity of biochar could optimize composting environment, accelerate the process of composting and facilitate microbial growth during the thermophilic composting stage, with increases of 1.3×10¹⁰ to 1.5×10¹¹cfu/g. Analysis of microstructure characterization of the changes in compost particle indicated that biochar amended contributed to better degradation of compost particle with smaller sizes and a higher degree of looseness. Ultimately, 10% biochar addition optimized organic matter degradation, while reducing ammonia and greenhouse gas emissions and costs.

Assessment of the occurrence, spatiotemporal variations and geoaccumulation of fifty-two inorganic elements in sewage sludge: A sludge management revisit

The limited information about the sludge quality has made its management a top environmental challenge. In the present study, occurrence and the spatiotemporal variations of 52 inorganic elements were investigated in the sludge samples from three wastewater treatment plants (WWTPs) in Xiamen city, China. The results showed, the occurrence of 49 elements with the concentrations in the range of >125-53500 mg kg^-1 dry sludge (DS) for commonly used industrial metals, 1.22-14.0 mg kg^-1 DS for precious metals, and 1.12-439.0 mg kg^-1 DS for rare earth elements. The geo-accumulation studies indicated a moderate to high levels of buildup of some elements in the sewage sludge. Principal components analysis (PCA) indicated strong spatial and weak temporal variations in the concentrations of the elements. Therefore, the sludge disposal operations, based on the element concentrations, geoaccumulation and economic potential are suggested for each WWTP. Sludge from W1 and W2 were found suitable for agricultural usage, while that from W3 showed a higher economic potential for the recovery of precious metals. This study concludes that a comprehensive analysis of the elements in the sewage sludge could provide critical information for the disposal and management of the sludge.

Role of biochar on composting of organic wastes and remediation of contaminated soils-a review

Biochar is produced by pyrolysis of biomass residues under limited oxygen conditions. In recent years, biochar as an amendment has received increasing attention on composting and soil remediation, due to its unique properties such as chemical recalcitrance, high porosity and sorption capacity, and large surface area. This paper provides an overview on the impact of biochar on the chemical characteristics (greenhouse gas emissions, nitrogen loss, decomposition and humification of organic matter) and microbial community structure during composting of organic wastes. This review also discusses the use of biochar for remediation of soils contaminated with organic pollutants and heavy metals as well as related mechanisms. Besides its aging, the effects of biochar on the environment fate and efficacy of pesticides deserve special attention. Moreover, the combined application of biochar and compost affects synergistically on soil remediation and plant growth. Future research needs are identified to ensure a wide application of biochar in composting and soil remediation. Graphical abstract ᅟ.

Assessment of Two Solid Anaerobic Digestate Soil Amendments for Effects on Soil Quality and Biosolarization Efficacy

Anaerobic digestion is an organic waste bioconversion process that produces biofuel and digestates. Digestates have potential to be applied as soil amendment to improve properties for crop production including phytonutrient content and pest load. Our objective was to assess the impact of solid anaerobic digestates on weed seed inactivation and soil quality upon soil biosolarization (a pest control technique that combines solar heating and amendment-induced microbial activity). Two solid digestates from thermophilic (TD) and mesophilic (MD) digesters were tested. The solarized TD-amended samples presented significantly higher mortality of Brassica nigra (71%, P = 0.032) than its equivalent incubated at room temperature. However, biosolarization with digestate amendment led to decreased weed seed mortality in certain treatments. The plant-available water, total C, and extractable P and K were significantly increased (P < 0.05) in the incubated amended soils. The results confirm the potential of digestates as beneficial soil amendments. Further studies are needed to elucidate the impacts of digestate stability on biosolarization efficacy and soil properties.

Seafood-Processing Sludge Composting: Changes to Microbial Communities and Physico-Chemical Parameters of Static Treatment versus for Turning during the Maturation Stage

In general, in composting facilities the active, or intensive, stage of the process is done separately from the maturation stage, using a specific technology and time. The pre-composted material to be matured can contain enough biodegradable substrates to cause microbial proliferation, which in turn can cause temperatures to increase. Therefore, not controlling the maturation period during waste management at an industrial level can result in undesired outcomes. The main hypothesis of this study is that controlling the maturation stage through turning provides one with an optimized process when compared to the static approach. The waste used was sludge from a seafood-processing plant, mixed with shredded wood (1:2, v/v). The composting system consists of an intensive stage in a 600L static reactor, followed by maturation in triplicate in 200L boxes for 112 days. Two tests were carried out with the same process in reactor and different treatments in boxes: static maturation and turning during maturation when the temperature went above 55°C. PLFAs, organic matter, pH, electrical conductivity, forms of nitrogen and carbon, hydrolytic enzymes and respiratory activity were periodically measured. Turning significantly increased the duration of the thermophilic phase and consequently increased the organic-matter degradation. PCA differentiated significantly the two treatments in function of tracking parameters, especially pH, total carbon, forms of nitrogen and C/N ratio. So, stability and maturity optimum values for compost were achieved in less time with turnings. Whereas turning resulted in microbial-group stabilization and a low mono/sat ratio, static treatment produced greater variability in microbial groups and a high mono/sat ratio, the presence of more degradable substrates causes changes in microbial communities and their study during maturation gives an approach of the state of organic-matter degradation. Obtaining quality compost and optimizing the composting process requires using turning as a control mechanism during maturation.

Comparative evaluation of aeration methods for municipal solid waste composting from the perspective of resource management: A practical case study in Tehran, Iran

During four months of practical composting examination, common aeration techniques including forced aeration static pile, pile turning, natural ventilation static pile and a combination of pile turning and natural ventilation static pile were investigated to determine the most appropriate method for a full-scale composting procedure using the organic fraction of Tehran's municipal solid wastes. The results of measured parameters such as temperature, pH, electrical conductivity (EC), C/N, and main nutrients including nitrogen, phosphorus and potassium suggested that both forced aeration and pile turning have efficacy in terms of final compost quality although pile turning showed better results for agricultural applications nevertheless significant energy consumption and pollutant emissions were associated with them. The combination of pile turning and natural ventilation could solve the problem of long degradation time and concurrently guarantee the acceptable quality of finished compost for agricultural purposes. Furthermore, this combinative method showed a specific energy consumption as low as 0.218 MJ per kg-dry and had a potential to save 288.8 kg-CO2/ha by applying the achieved compost on the farm in order to replace the chemical fertilizers.

Evaluation of calcium cyanamide addition during co-composting of manure and maize straw in a forced-aeration static-pile system

BACKGROUND

Composting is one of the most environmentally friendly treatments to inactivate pathogenic organisms or reduce them to acceptable levels. However, even under thermal conditions, some pathogenic organisms such as E. coli could exist for a long time in composting. Such great persistence may increase the possibility of outbreaks of these organisms and further increase the environmental load. Calcium cyanamide (CaCN₂) has recently been recognized to have the fungicidal effect on the pathogens of the soilborne diseases. So, the present study determined the effect of CaCN₂ addition on composting progress as an antimicrobial agent and an amendment during forced-aeration static-pile composting of cow manure, which was mainly aimed to inhibit the pathogens that had not been inactivated by heat during composting.

METHODS

The mixtures of dairy cow manure and maize straw with addition of 2 % CaCN₂ or no addition were composted for 63 days. The physical, chemical and biological changes in compost mixtures were examined during composting. The data were statistically analyzed using ANOVA procedure from SAS software (version 9.0).

RESULTS

The results showed that the addition of CaCN₂ significantly increased the maximum temperature and lengthened the duration of the thermophilic phase, and increased the percent T-N but decreased C/N ratio. For microbiological test, the addition of CaCN₂ shortened the time to inactivate E. coli, and increased the total average population of thermophilic bacteria but did not significantly influence that of mesophilic bacteria.

CONCLUSION

The results indicated that the addition of CaCN₂, at least at the additive content of 2 % could benefit the thermophilic phase and the composting could quickly reach the sanitary standard during the composting of manure with maize straw in a forced-aeration static-pile system. This finding will contribute to solve the feces disposal problems.