Composting of pig manure and forest green waste amended with industrial sludge

The maturity, humus content, and microbial metabolic function of sheep manure compost on the Qinghai-Tibet Plateau can be significantly improved by reducing the moisture content

The Qinghai-Tibet Plateau (QTP) is characterized by an extreme hypoxia, which may lead to lack of sufficient oxygen for compost production, and thus seriously affecting the compost quality. The moisture content (MC) has a direct effect on the oxygen content of composting pile. At present, the research on the optimum moisture content of compost production on the QTP is still lacking. This study aimed to investigate the influences of MC on fermentation quality of sheep manure composting on the QTP and to further analyze the changes of microbial metabolic function and enzyme activity under different MC. Composting experiment with low MC (45%) and conventional MC (60%) was conducted in both summer and autumn. The results showed that the composting efficiency of 45% MC was better than 60% in both seasons, which was mainly manifested as longer high-temperature period (summer:16 d vs 14 d, autumn: 7 d vs 2 d), higher germination index (summer:136.1% vs 128.6%, autumn:103.5% vs 81.2%), and more humus synthesis (summer:159.8 g/kg vs 151.2 g/kg, autumn:136.1 k/kg vs 115.5 k/kg). The 45% MC can improve microbial metabolism, including increasing the abundance of functional genes involved in carbohydrate metabolism, amino acid metabolism, and nucleotide metabolism and improving the activities of cellulase, β-glucosidase, protease, polyphenol oxidase, and peroxidase. In conclusion, 45% MC can improve the fermentation efficiency and products quality of sheep manure compost on QTP.

Effects of turning frequency on fermentation efficiency and microbial community metabolic function of sheep manure composting on the Qinghai-Tibet Plateau

This study explored the effects of turning frequency on fermentation efficiency and microbial metabolic function of sheep manure composting on the Qinghai-Tibet Plateau (QTP). Five treatments with different turning frequencies were set up in this study: turning every 1 day (T1), 2 days (T2), 4 days (T3), 6 days (T4), and 8 days (T5). Results showed that the high temperature period for T1 and T5 lasted only 4 days, while that for T2-T4 lasted more than 8 days. The germination index of T1 and T5 was lower than 80%, while that of T2-T4 was 100.6%, 97.8%, and 88.6%, respectively. This study further predicted the microbial metabolic function of T2-T4 using the bioinformatics tool PICRUSt2 (Phylogenetic Investigation of Communities by Reconstruction of Unobserved States) and determining the activities of various functional enzymes. The results showed that carbohydrate metabolism, protein metabolism, and nucleotide metabolism were the main metabolic pathways of microorganisms, and that T2 increased the abundance of functional genes of these metabolic pathways. The activities of protease, cellulase, and peroxidase in T2 and T3 were higher than those in T4, and the effect of T2 was more significant. In conclusion, turning once every 2 days can improve the quality of sheep manure compost on the QTP.

Evaluation of a cascade artificial neural network for modeling and optimization of process parameters in co-composting of cattle manure and municipal solid waste

The present study was carried out to improve, test, and validate the Cascade Forward Neural Network (CFNN) for co-composting of municipal solid waste (MSW) and cattle manure (CM). Composting was performed in vessel pilot-scale reactors with different CM rates for 105 days. The CFNN used 5 input variables containing CM and MSW mixture combinations, and 1 output for each of the compost quality parameters. The CFNN results were compared with Response Surface Methodology (RSM) and Feed Forward Neural Network (FFNN) results. Multi-objective optimization process using Genetic Algorithm (GA), the total desirability, which has a much better value than the RSM, was obtained as 0.4455 and the CM ratio and processing time were determined as approximately 23.39% and 104.86 days, respectively. It is concluded that CFNN is a unique modeling tool, exhibiting superior modeling and prediction performance in MSW and compost modeling for CM.

Promoting lignocellulose degradation during green waste composting by maintaining a specific temperature through heap size control

Owing to its high lignocellulose content, the recalcitrance of green waste is a technical challenge obstructing the composting process. This study aimed to identify a temperature that could facilitate efficient lignin and cellulose degradation during green waste composting, and maintain this temperature by controlling the heap size to enhance the degradation. The optimum temperature was determined by conducting a laboratory-scale cultivation experiment under controlled temperatures, and a pilot-scale experiment was conducted to explore heap size control and its influence on green waste composting. The results showed that efficient lignin and cellulose degradation was achieved when the temperature was between 45 and 60 ℃, and maintaining this temperature for at least 150 days maximized the lignin and cellulose degradation rates. This was achieved by constraining the heap size at 0.8 m³ at the beginning of composting; 1.56, 2.60, and 4.00 m³ on days 15, 39, and 96; and then enlarging the heap as much as possible on day 156. Following this approach, the duration of the target temperature was extended by over six times, the lignin and cellulose degradation rates were increased by 18.82-21.38 % and 9.54-11.55 %, and nitrification and humification were enhanced. Correlation analysis showed that lignocellulose degradation, nitrification, and humification were positively and significantly correlated with the duration of the target temperature. Generally, heap size control is an ecological and economic method of enhancing the efficiency and quality of green waste composting and compost, respectively.

Steam-Exploded Pruning Waste as Peat Substitute: Physiochemical Properties, Phytotoxicity and Their Implications for Plant Cultivation

Peat is a nonrenewable resource that we are using at alarming rates. Development of peat alternative from pruning waste (PW) could be a cost- and environment-friendly way of disposal. Steam explosion (SE) is a commonly used pretreatment of lignocellulosic biomass, but its impact on the properties of PW as a growing substrate is largely unknown. To address this issue, PW was treated using five SE temperatures (160, 175, 190, 205 and 220 °C) and three retention times (1, 3 and 5 min) and evaluated for key traits of growing substrate. Results indicate that bulk density, total porosity, EC, total carbon, and concentration of phytotoxins including phenol, flavonoid, and alkaloid significantly increased or tended to increase with increasing temperature and/or retention time. A reversed trend was observed for water-holding capacity, pH, content of hemicellulose and lignin, and germination index. Cation exchange capacity and total N showed minimal response to SE. Steam explosion had inconsistent impacts on acid soluble nutrients. Phytotoxicity was a major factor limiting the use of SE-treated PW as growing substrate. Higher pretreatment severity led to higher phytotoxicity but also facilitated subsequent phytotoxicity removal by torrefaction. Pruning waste treated by SE and torrefaction under certain conditions may be used as peat substitute for up to 40% (v/v).

Co-composting of forest and industrial wastes watered with pig manure

Co-composting of forest-derived wastes (chestnut forest burr, CST; scrubland biomass, SRB; industrial sludge, MDFS, from the Medium Density Fibreboard production process) watered with pig manure (PM) may constitute a feasible management technique for both solid and liquid streams. PM provided water and improved the carbon to nitrogen (C/N) ratio. Four piles of 1.8-2.4 m³ were conformed: A (SRB, with compaction bulk density), B (SRB, without compaction), C (SRB and MDFS at a volumetric ratio of 3:1) and D (CST). Thermophilic temperatures were maintained for 8 (B), 16 (A), 28 (C) and 40 (D) days. Stable compost was obtained after 35 (A, B, C) and 48 (D) days. Hygienization was only complete in piles C and D. N losses were higher in piles A (39.3%) and B (33.6%) in relation to C (17.0%) and D (8.9%) which could be attributed to the characteristics of MDFS and CST. Increasing the matrix size from 340 L to around 2000 L led to a higher intensity of the thermophilic phase. Besides, compaction significantly increased the temperature during composting. PM was added at ratios ranging from 1.8 to 2.5 L/kg dry matter, being favoured by pre-drying of solid wastes.

Cleaner production of agriculturally valuable benignant materials from industry generated bio-wastes: A review

Bio-wastes from different agro-based industries are increasing at a rapid rate with the growing human population's demand for the products. The industries procure raw materials largely from agriculture, finish it with the required major product, and produce huge bio-wastes which are mostly disposed unscientifically. This creates serious environmental problems and loss of resources and nutrients. Traditional bio-wastes disposal possess several demerits which again return with negative impact over the eco-system. Anaerobic digestion, composting, co-composting, and vermicomposting are now-a-days given importance due to the improved and modified methods with enhanced transformation of bio-wastes into suitable soil amendments. The advanced and modified methods like biochar assisted composting and vermicomposting is highlighted with the updated knowledge in the field. Hence, the present study has been carried to compile the effective and efficient methods of utilizing industry generated bio-wastes for circularity between agriculture - industrial sectors to promote sustainability.

Ceramic membrane-based ultrafiltration combined with adsorption by waste derived biochar for textile effluent treatment and management of spent biochar

PURPOSE

Effluents produced in the textile industries are important sources of water pollution due to the presence of toxic dyes, auxiliary chemicals, organic substances etc. Recycling of such industrial wastewater is one major aspect of sustainable water management; hence present study is focused on an eco-friendly process development for reclamation of higher loading textile wastewater.

METHOD

Industrial effluent samples with varying loading were collected from textile processing units located in and around Kolkata city. Vegetable waste collected from local market was utilized to prepare an efficient biochar for elimination of the recalcitrant dyes. Prior to adsorption, ceramic ultrafiltration (UF) process was used for reduction of the organic loading and other suspended and dissolved components.

RESULTS

A remarkably high BET surface area of 1216 m²g^-1 and enhanced pore volume of 1.139 cm³g^-1 was observed for biochar. The maximum adsorption capacity obtained from the Langmuir isotherm was about 300 mg.g^-1. The combined process facilitated >99% removal of dyes and 77-80% removal of chemical oxygen demand (COD) from the various samples of effluent. The treated effluent was found suitable to discharge or reuse in other purposes. About 95% of dye recovery was achieved during biochar regeneration with acetone solution. The dye loaded spent biochar was composted with dry leaves and garden soil as bulking agent. Prepared compost could achieve the recommended parameters with high nutritional value after 45 days.

CONCLUSIONS

The overall study showed potential of the proposed process towards treatment of toxic dye loaded textile effluent in an environment friendly and sustainable approach.

Aeration requirement and energy consumption of reactor-composting of rose pomace influenced by C/N ratio

As the composting industry develops rapidly in the world, the compost producers have focused on the efficiency of energy utilization in production without restricting the quality of compost in the forced ventilation systems. Therefore, this experimental study quantified the impacts of initial C/N ratio on aeration requirement and energy consumption due to aeration for reactor composting of rose pomace through kinetics of the process using fifteen 100-l composting reactors. The results of the study showed that initial C/N ratio significantly affected decomposition rate, compost maturity, and dry matter losses and organic matter losses (P < 0.05). The maximum decomposition rate (0.072 day^-1) and the highest degree of progression of the composting process existed at the mixture with initial C/N ratio of 24.26. The results underlined the importance of the initial C/N of composting of rose pomace in terms of energy consumption due to aeration. In particular, more mature compost within a short time can be obtained when composting was operated with a C/N ratio of 23.7-25.8 in the expense of requiring more airflow rate, fan power, and energy consumption by aeration fan per composting material.

Co-composting of sewage sludge and Phragmites australis using different insulating strategies

Insulating strategies are indispensable for laboratory-scale composting reactors, however, current insulation methods interfere with the aerobic fermentation behaviors related to composting. To address this issue, a centre-oriented real-time temperature compensation strategy was designed in this study. Five 9 L reactors (R1-R5) with different insulation strategies were used for the co-composting of dewatered sludge and Phragmites australis and compared. The process performance was assessed by monitoring the temperature, O₂ and CO₂ emissions, the physical-chemical properties of the composting materials were evaluated by measuring the organic matter (OM), carbon nitrogen ratio (C/N), pH, electrical conductivity (EC), and fluorescence excitation-emission matrix (EEM) spectra. And a 16S rDNA analysis was used to quantify the evolution of bacterial community. The main findings are as follows. Compared with R1 as a control, the insulating strategies can increase the maximum temperature and prolong the thermophilic phase of composting. Comparing R1 and R3 showed that real-time temperature compensation can better restore the real fermentation of the compost. The results showed that R5 had the best composting effect, reaching 69.8 °C, which was 25.1%, 29.7%, 19.3%, and 17.3% higher than R1, R2, R3, and R4, respectively, and remaining in the thermophilic phase for 4.24 d, which is 1.4, 1.5, 1.3, and 0.2 times longer than R1, R2, R3, and R4, respectively. Furthermore, it can significantly reduce the temperature difference between the centre and edge of the reactor, which improved the composting material allocation efficiency and composting process control accuracy, further providing a basis for the actual full-scale composting operation.

Biodegradation of polyaromatic hydrocarbons and the influence of environmental factors during the co-composting of sewage sludge and green forest waste

The main aim of this research was to study the biodegradation of polycyclic aromatic hydrocarbons (PAHs) and the influence of environmental factors during composting in order to realize the utilization of PAHs contaminated sewage sludge. A production scale compost experiment was conducted with three mixtures of sewage sludge (SS): green forest waste (GFW) at quality ratios of 3:1 (T1), 3:2 (T2) and 3:3 (T3). The residual concentration of PAHs in the three treatments met the permissible limit prescribed by the Agricultural Sludge Pollutant Control Standard (GB 4284-2018). The biodegradation rates of PAHs were 0.0280, 0.0281 and 0.0218 mg/d, and removal efficiencies were 70.7%, 75.2% and 62.4% in T1, T2, T3, respectively, which followed the first-order rate kinetics. The residual concentration of PAHs in T2 was the lowest (1.81 mg/kg), while the germination index (GI) of Tall Fescues (~0.9) was the highest during 50 days of co-composting. The bacterial diversity negatively correlated with the residual PAHs content. The main genus, Bacillus, Pseudomonas and Methylotenera, with cellulose-degrading and PAHs co-metabolizing functions contributed significantly to sludge maturation and PAHs degradation. The dominant microorganisms, Pseudomonas, Sphingobacterium and Chitinophagaceae_uncultured, could support the high removal rate of PAHs in T2. Temperature, pH, total organic carbon (TOC), total nitrogen (TN) and carbon/nitrogen (C/N) ratio had significant positive effect on the compost maturity and quality, and these parameters correlated with the PAHs biodegradation efficiency during composting, especially in T2.

Degradation mechanism of lignocellulose in dairy cattle manure with the addition of calcium oxide and superphosphate

Cellulose and lignin belongs to refractory organic matters in the traditional composting. In this research, the degradation of lignocellulose in dairy cattle manure was investigated through adding calcium oxide (CaO) and superphosphate (SSP). In the presence of CaO and SSP, the degradation rate of cellulose and lignin were improved by 25.0% and 8.33%, respectively. The results indicated that the pH value in system would be slightly higher with the addition of CaO and SSP. Besides, the pH value of all cow manure piles were about 8.4 after composting rotten, which could be well neutralized by the gradually acidified soil in the southwest of China with the full effect of fertilizer released. In addition, the abundance of Bacillales, Actinomycetes, and Thermoactinomycetaceae in the experimental groups (AR) was slightly better than that in the control groups (CK) during composting, which led to a conclusion that an elaborate physical-chemical-multivariate aerobic microorganism evolution model of cellulose degradation products (PCMC) was deduced and the physical-chemical-multivariate aerobic microorganism model of lignin cycle degradation (PCML) was developed.

Multivariate insights of bulking agents influence on co-biodrying of sewage sludge and food waste: Process performance, organics degradation and microbial community

As a prerequisite additive, bulking agent played an essential role on organic wastes biodrying by affecting the organics degradation and microbial consortia. In this study, a series of experiments were conducted to explore the relationships among the type of bulking agents, organics degradation and microbial community evolution. In line with the excellent physiochemical properties, corncob was found to be more desirable for biodrying with more water removal (62.13% vs. 53.70% for sawdust and 51.72% for straw) and higher energy efficiency. Furthermore, different bulking agents showed different biodegradability and affected co-existed organics degradation. In detail, corncob upgraded the amylase and lipase activities, thus promoting the degradation of readily degradable carbohydrates and lipids in feedstocks, which accounted for >60% of the bio-heat sources for water evaporation. In addition, pyrosequencing analysis revealed that Bacillus (>50%) and Ochrobactrum (>40%) were the dominant genera in thermophilic and cooling phases, with degradation capacities of readily degradable substrate and lignocellulose, respectively. And the pathogens, e.g., E. coli and K. pneumonia, were seriously inhibited by high matrix temperatures in corncob trial. These results not only suggested the corncob was a promising bulking agent, but the potential microbial mechanisms for organics degradation were also revealed.

Impact of carbonatation lime addition on composting of vegetable oil refining sludge

The aim of the present work is to evaluate how the vegetable oil refining sludge produced by the agro-food industry could be composted using carbonatation lime and green waste as bulking agents. To achieve this goal, three windrows were prepared with different mixtures: windrow 1 contained oil sludge and green waste (20:10 on a wet mass basis) while windrow 2 contained oil sludge, green waste and carbonatation lime (20:10:10, on a wet mass basis). The composition of windrow 3 was: oil sludge, green waste and carbonatation lime (20:10:20, on a wet mass basis). The results showed that the use of carbonatation lime for composting vegetable oil refining sludge was able to regulate the high acidity of the sludge and thus to obtain an optimal pH value for the launching and maintenance of the composting process. The addition of carbonatation lime also gave better reduction of microbial activity without any negative effect on composting. The compost prepared with oil refining sludge (49% fresh mass), carbonatation lime (27%) and green waste (24%) exhibited the best quality with C/N ratio and pH values within the norm NFU44-051. These promising results could be a sustainable solution for the valorization of both oil refining sludge and sugar carbonatation lime.

Biotransformation of flower waste composting: Optimization of waste combinations using response surface methodology

Flower waste (FW) is disposed off in the rivers or mixed with solid waste for landfilling that pollutes the environment and causes harmful effects on human health and aquatic life. It is rich in nutrient content and easily converted into the compost. Therefore, the objective of the present research was to optimize the combinations of flower waste and cow dung during agitated pile composting using response surface methodology. Thirteen different agitated piles were used for composting using the central composite design. The optimum combination from central composite design was 65 kg floral waste, 25 kg cattle dung and 10 kg sawdust having 7.10 pH, 3.31 mS cm^-1 electrical conductivity, 32.98% total organic carbon and 14 Carbon to Nitrogen ratio during the end phase of the composting period. The nutrient concentrations into the final compost were within the acceptable limit and also found to be beneficial for the growth of plants.

Co-biodrying of sewage sludge and organic fraction of municipal solid waste: Role of mixing proportions

This study investigated the performance of co-biodrying sewage sludge and organic fraction of municipal solid waste (OFMSW) at different proportions. Cornstalk was added at 15% (of total wet weight) as the bulking agent. Results show that increasing OFMSW percentage promoted the biodegradation of organic matter, thus enhancing the temperature integration value and water removal to above 75% during sludge and OFMSW co-biodrying. In particular, adding more OFMSW accelerated the biodegradation of soluble carbohydrates, lignins, lipids, and amylums, resulting in more organic loss and thus lower biodrying index (3.3-3.7 for 55-85% OFMSW). Water balance calculation indicated that evaporation was the main mechanism for water removal. Heat used for water evaporation was 37.7-48.6% of total heat consumption during co-biodrying. Our results suggest that sludge and OFMSW should be mixed equally for their efficient co-biodrying.

A systematic review on the composting of green waste: Feedstock quality and optimization strategies

Green waste (GW) is an important fraction of municipal solid waste (MSW). The composting of lignocellulosic GW is challenging due to its low decomposition rate. Recently, an increasing number of studies that include strategies to optimize GW composting appeared in the literature. This literature review focuses on the physicochemical quality of GW and on the effect of strategies used to improve the process and product quality. A systematic search was carried out, using keywords, and 447 papers published between 2002 and 2018 were identified. After a screening process, 41 papers addressing feedstock quality and 32 papers on optimization strategies were selected to be reviewed and analyzed in detail. The GW composition is highly variable due to the diversity of the source materials, the type of vegetation, and climatic conditions. This variability limits a strict categorization of the GW physicochemical characteristics. However, this research established that the predominant features of GW are a C/N ratio higher than 25, a deficit in important nutrients, namely nitrogen (0.5-1.5% db), phosphorous (0.1-0.2% db) and potassium (0.4-0.8% db) and a high content of recalcitrant organic compounds (e.g. lignin). The promising strategies to improve composting of GW were: i) GW particle size reduction (e.g. shredding and separation of GW fractions); ii) addition of energy amendments (e.g. non-refined sugar, phosphate rock, food waste, volatile ashes), bulking materials (e.g. biocarbon, wood chips), or microbial inoculum (e.g. fungal consortia); and iii) variations in operating parameters (aeration, temperature, and two-phase composting). These alternatives have successfully led to the reduction of process length and have managed to transform recalcitrant substances to a high-quality end-product.