Performance of co-composting sewage sludge and organic fraction of municipal solid waste at different proportions

Impact of mesophilic co-composting conditions on the quality of substrates produced from winery waste activated sludge and grape stalks: Lab-scale and pilot-scale studies

In this study, different amounts of a mixture of winery waste activated sludge and grape stalks were co-composted for 8 weeks, at lab-scale under different temperatures and aeration rates, and at pilot-scale. None of the experiments showed the occurrence of a thermophilic stage, even when the composting temperature was kept at 34 °C, which might suggest biological suppression by the acclimated mesophilic microorganisms ubiquitous to the winery waste activated sludge. The composted substrates were fully characterized by physicochemical analysis, plant growth tests and germination indexes using parsley (Petroselinum crispum) seedlings and seeds. Surprisingly, despite the higher volume reduction at lab-scale, it was the initial mixture and the mixture composted outdoors which presented the best horticultural qualities, with seedling survival rates of 88.9% and 87.0% and modified germination indexes of 54% and 161%, respectively. These findings shed some light on previous contradictory results and allow the development of new recycling strategies.

Microbial inoculation influences bacterial community succession and physicochemical characteristics during pig manure composting with corn straw

This study determined the physicochemical changes and bacterial community succession in the pig manure composting process with microbial inoculant. Microbial inoculant could prolong the thermophilic stage by 2 days and increased the germination index (GI). Analysis with 16S rDNA showed that the Chao1 and Shannon indices increased at the thermophilic stage in the treatment (T), while those of the control (C) decreased. Microbial inoculant increased the relative abundance of Flavobacterium and Solibacillus in 4-12 and 12-24 days, respectively. Acinetobacter was reduced at 4-12 days. The key physicochemical factors affecting microbial successions were revealed by canonical correspondence analysis (CCA) and correlation analysis. Linear discriminant analysis (LDA) effect size (LEfse) analysis showed that there were 78 biomarkers, while in piles T and C, there were 35 and 43 biomarkers, respectively. These results indicated the addition of microbial inoculant improved the maturity and fertility, as well as significantly regulating the microbial community structure.

Influence of FeONPs amendment on nitrogen conservation and microbial community succession during composting of agricultural waste: Relative contributions of ammonia-oxidizing bacteria and archaea to nitrogen conservation

Composting amended with iron oxide nanoparticles (FeONPs, α-Fe₂O₃ and Fe₃O₄ NPs) were conducted to study the impacts of FeONPs on nitrogen conservation and microbial community. It was found that amendment of FeONPs, especially α-Fe₂O₃ NPs, reduced total nitrogen (TN) loss, and reserved more NH₄⁺-N and mineral N. Pearson correlation analysis revealed that decrease of ammonia-oxidizing bacteria (AOB) in FeONPs treatments played more important role than ammonia-oxidizing archaea (AOA) in reserving more NH₄⁺-N and mineral N, and reducing TN loss. Bacterial community composition at phylum level did not shift with addition of FeONPs. Firmicutes, Actinobacteria, and Proteobacteria were the three most dominant phyla in all treatments. Overall, this study provides a method to reduce TN loss and improve mineral N reservation during composting, and gives a deep insight into the role of AOB and AOA in nitrogen transformation.

Crop-based composting of lignocellulosic digestates: Focus on bacterial and fungal diversity

In this study, organic matter degradation and microbial diversity were assessed during the composting of lignocellulose-rich digestates. Digestates were collected based on each crop type during anaerobic co-digestion of cow manure and barley, triticale, wheat and rye. Bacterial and fungal diversity in digestate composting systems were determined by 16S and 18S rRNA gene amplicon sequencing, respectively. Crop-based composting of anaerobic digestates showed similar process trends in terms of pH, temperature, moisture content (MC) and C:N ratio. The properties of final compost products were in accordance with the national legislations regarding soil applications, except MC, which were therefore air-dried before being amended to soil. Most abundant bacterial genera were represented by Luteimonas, Bacillus, Ochrobactrum and Thermobifida. Meanwhile, Thermomyces, Aspergillus, Galactomyces and Neurospora were detected as the predominant fungal genera in all compost samples.

Co-biodrying of sewage sludge and organic fraction of municipal solid waste: A thermogravimetric assessment of the blends

This study investigated the thermogravimetric properties of sewage sludge and organic fraction of municipal solid waste (OFMSW) during their co-biodrying at different fractions. Sewage sludge and OFMSW were co-biodried at the mass proportion of 0%, 42.5% and 85% (of the total wet weight), respectively, with 15% cornstalk as the bulking agent. Results show that of these three raw materials, OFMSW exhibited the lowest ignition temperature and the highest burnout temperature. Moreover, OFMSW had a better comprehensive combustion performance (S) than sewage sludge. Blending OFMSW, sewage sludge and cornstalk showed the highest S value (4.0 × 10^-7%² min^-2 °C^-3). In addition, there existed certain interactions between the co-combustion process, especially at high temperature stage. The burning characteristics, including ignition performance, burnout efficiency, DTG_max and S increased with fluctuations in the first 6-9 days of co-biodrying process, and then declined in all treatments. Hence, 15-day of biodrying made the product with poor burning behavior (S value of 1.0 × 10^-7-1.4 × 10^-7%² min^-2 °C^-3). More importantly, the optimal combustion performance was observed when co-biodrying the same amount (42.5%) of sewage sludge and OFMSW with the peak of 8.3 × 10^-7%² min^-2 °C^-3 achieved on day 9. In addition, the blends were easier to burn after the biodrying process.

Impacts of iron oxide nanoparticles on organic matter degradation and microbial enzyme activities during agricultural waste composting

The effects of iron oxide nanoparticles (IONPs, including Fe₂O₃ NPs and Fe₃O₄ NPs) on composting were investigated through evaluating their influences on organic matter (OM) degradation, dehydrogenase (DHA) and urease (UA) activities, and quality of the final compost product. Results showed that composting amended with Fe₂O₃ NPs was more effective to facilitate OM degradation. At the end of composting, the total OM loss in T-C, T-Fe₂O₃ NPs and T-Fe₃O₄ NPs was 66.19%, 75.53% and 61.31%, respectively. DHA and UA were also improved on the whole by the amendment of IONPs, especially Fe₂O₃ NPs. Although relationships between enzyme activities and environmental variables were changed by different treatments, temperature was the most influential to variations of both DHA and UA in all treatments, which independently explained 75.1%, 34.7% and 38.4% of variations in the two enzyme activities in T-C, T-Fe₂O₃ NPs and T-Fe₃O₄ NPs, respectively. Compared with DHA, UA was more closely related to the environmental parameters. The germination index in T-C, T-Fe₂O₃ NPs and T-Fe₃O₄ NPs was 134.49%, 153.64% and 146.76%, and the average shoot length was 3.16, 3.87 and 3.45 cm, respectively, indicating that amendment of IONPs, especially Fe₂O₃ NPs, could promote seed germination and seedling growth. Therefore, composting amended with IONPs was a feasible and promising method to improve composting performance, enzyme activities as well as quality of the final compost product.

Socioeconomic, agricultural, and individual factors influencing farmers' perceptions and willingness of compost production and use: an evidence from Wadi al-Far'a Watershed-Palestine

In Palestine, open dumping and/or burning the waste, including agricultural waste, are prevalent practices resulting in emitting leachate and acidifying greenhouse gases. Composting the agricultural waste can reduce emissions and provide 'compost' as an organic fertilizer and soil amendment; yet, it has not been implemented at the national level. To develop a local marketing strategy for compost, this study views a need to identify farmers' perceptions and willingness of compost production and use in agriculture and examine various socioeconomic, agricultural, and individual factors shaping them. The case of Wadi al-Far'a watershed (WFW) is investigated, where farmers practice inappropriate waste disposal and overuse of agrochemicals. A semi-structured questionnaire is administered to 409 farmers through face-to-face interviews. Descriptive statistics, bivariate analyses, Chi-square test, and binary logistic regression are used for data analysis. High acceptance level (84%) is disclosed among farmers in WFW for the hypothetical idea of producing and using compost. Farmers also have high, yet lower, willingness level (63.6%) of the more salient option of producing compost themselves and using it in agriculture. Tenure systems, large cultivated areas, rainfed irrigation, and lack of access to training sessions inhibit farmers' acceptance of the idea of compost production (overall p value = 0.000). Large cultivated areas and rainfed irrigation is also associated with farmers' unwillingness to produce compost, besides high household monthly income, animal or mixed animal-plant farming, experience in compost production, and use of pesticides (overall p value = 0.000).

Performance evaluation of gaseous emissions and Zn speciation during Zn-rich antibiotic manufacturing wastes and pig manure composting

In this study, the co-composting performance of Zn-rich antibiotic manufacturing wastes (AMW) and pig manure (PM) was evaluated. Four treatments, representing 2.5%, 5%, 10% and 20% of AMW (of PM dry weight) and control without AMW, were established during composting. Results suggested that the temperature, pH, electrical conductivity, NH₄⁺-N and germination index in end product met the maturity and sanitation requirement. More than 99% of residual antibiotic was removed. Compared with PM composting alone, the cumulative CH₄ and N₂O emissions in AMW composting increased by 13.46-79.00% and 10.78-65.12%, respectively. While the higher mixing ratios of AMW (10% and 20%) presented a negative impact on composing by inhibiting organic matter (OM) degradation and higher NH₃ emissions. The AMW had highly bioavailable Zn, but the exchangeable faction of Zn significantly decreased with the composting progress.

The Evaluation of Hazards to Man and the Environment during the Composting of Sewage Sludge

Composting is considered an effective treatment option to eliminate or substantially reduce potential hazards relating to the recycling of sewage sludge (SS) on land. The variation of four major types of hazards (heavy metals, instability, pathogenic potential and antibiotic resistance) was studied during laboratory-scale composting of two mixtures of sludge and green waste (1:1 and 1:2 v/v). The heavy metal content of the final compost was governed by the initial contamination of SS, with the bulking agent ratio having practically no effect. The composts would meet the heavy metal standards of the United States of America (USA) and the European Union member states, but would fail the most stringent of them. A higher ratio of bulking agent led to a higher stabilisation rate, nitrogen retention and final degree of stability. A good level of sanitisation was achieved for both mixtures, despite the relatively low temperatures attained in the laboratory system. The antibiotic resistance was limited among the E. coli strains examined, but its occurrence was more frequent among the Enterococcus spp. strains. The type of antibiotics against which resistance was mainly detected indicates that this might not be acquired, thus, not posing a serious epidemiological risk through the land application of the SS derived composts.

Effect of semi-permeable cover system on the bacterial diversity during sewage sludge composting

Sewage sludge composting is a profitable process economically viable and environmentally friendly. In despite of there are several kind of composting types, the use of combined system of semipermeable cover film and aeration air-floor is widely developed at industrial scale. However, the knowledge of the linkages between microbial communities structure, enzyme activities and physico-chemical factors under these conditions it has been poorly explored. Thus, the aim of this study was to investigate the bacterial dynamic and community structure using next generation sequencing coupled to analyses of microbial enzymatic activity and culturable dependent techniques in a full-scale real composting plant. Sewage sludge composting process was conducted using a semi-permeable Gore-tex cover, in combination with an air-insufflation system. The highest values of enzymatic activities such as dehydrogenase, protease and arylsulphatase were detected in the first 5 days of composting; suggesting that during this period of time a greater degrading activity of organic matter took place. Culturable bacteria identified were in agreement with the bacteria found by massive sequencing technologies. The greatest bacterial diversity was detected between days 15 and 30, with Actinomycetales and Bacillales being the predominant orders at the beginning and end of the process. Bacillus was the most representative genus during all the process. A strong correlation between abiotic factors as total organic content and organic matter and enzymatic activities such as dehydrogenase, alkaline phosphatase, and ß-glucosidase activity was found. Bacterial diversity was strongly influenced by the stage of the process, community-structure change was concomitant with a temperature rise, rendering favorable conditions to stimulate microbial activity and facilitate the change in the microbial community linked to the degradation process. Moreover, results obtained confirmed that the use of semipermeable cover in the composting of sewage sludge allow a noticeable reduction in the process-time comparing to conventional open windrows.