Co-composting Of Sewage Sludge Research Articles

Co-composting of sewage sludge as an effective technology for the production of substrates with reduced content of pharmaceutical residues

Sewage sludge is a valuable source of elements such as phosphorus and nitrogen. At the same time, heavy metals, emerging organic compounds, micropollutants (pharmaceuticals, pesticides, PCPs, microplastics), or some potentially dangerous bacteria can be present. In this study, the sewage sludge was aerobically treated by composting with other materials (co-composted), and the resulting substrate was tested for suitability of its use in agriculture. Closer attention was focused on the pharmaceuticals (non-steroidal antiphlogistics, sartanes, antiepileptics, caffeine, and nicotine metabolites) content and ecotoxicity of the resulting substrates in the individual phases of sludge co-composting. It has been verified that during co-composting there is a potential for reduction of the content of pharmaceutical in the substrates up to 90 %. The course of the temperature in the thermophilic phase is decisive. Growth and ecotoxicity experiments demonstrated that with a suitable co-composting procedure, the resulting stabilized matter is suitable as a substrate for use in plant production, and the risk of using sewage sludge on agricultural land is substantially reduced.

The high dose of biochar reduces polycyclic aromatic hydrocarbons losses during co-composting of sewage sludge and wheat straw

The aim of the study was to investigate the effect of the biochar (BC) dose on solvent extractable (Ctot) and freely dissolved (Cfree) polycyclic aromatic hydrocarbons (PAHs) content during co-composting. A significantly better reduction of Σ16 Ctot PAHs after 98 days occurred during composting with BC (for 1% of BC – 44% and for 5% of BC – 23%) than in the control (15%). Despite the relatively high reduction of Ctot PAHs in the experiment with 5% BC rate, the content of the PAHs was still the highest compared to other variants. Regarding Cfree PAHs, 5% rate of BC resulted in the best reduction of PAHs, while the 1% BC dose resulted in a lower reduction of Cfree than the control. For 1% BC, PAHs losses was more effective, and sequestration processes played a less significant role than in the experiment with 5% dose of BC. The total and dissolved organic carbon, and ash were predominantly responsible for Ctot and Cfree losses, and additionally pH for Cfree. The results of the experiment indicate that BC performs a crucial role in composting, affecting the Ctot and Cfree PAHs in the compost but the final effect strictly depends on the BC dose.

Co-composting of sewage sludge with plant biomass, and analysis of microbiome relevant to plant growth promotion

In this study, a pilot-scale co-compositing process using sewage sludge and plant biomass in Japan was used as a model for a local circular bioeconomy. Heavy metal concentrations in the developed sewage sludge compost (NSSC) were lower than the threshold values of composts reported worldwide, and the fiber content was higher (33.6 %) than that of commercial sewage sludge compost (CSSC) (9.7 %), indicating that co-composting with plant biomass resolves the issues associated with sewage sludge. Komatsuna (Brassica rapa var. peruviridis) showed plant growth-promoting effects after fertilizing with NSSC compared to CSSC. The alpha diversities of NSSC were 4- to 6-fold higher than those of CSSC, and several effective biosynthetic gene clusters, such as non-ribosomal peptide synthases, siderophores, and acetoin metabolism, were detected in the predominant microorganisms, suggesting that NSSC may promote plant growth owing to an increase in the presence of antagonistic microorganisms and promotion of microbial interactions in the soil.

Co-composting of Sewage Sludge, Green Waste, and Food Waste

Article by Dijana Grgas, Tea Štefanac, Martina Barešić, Merima Toromanović, Jasmina Ibrahimpašić, Tomislava Vukušić Pavičić, Mirna Habuda-Stanić, Zoran Herceg and Tibela Landeka Dragičević published in JSDEWES

Impact of different structures of biochar on decreasing methane emissions from sewage sludge composting.

Methane (CH4) emissions from sewage sludge composting can be reduced by using biochar more effectively. This study investigates the impact of different structure of biochar on CH4 emissions during sewage sludge composting. Corncob biochar (CB, pore size = 35.3990 nm), rice husk biochar (RB, pore size = 3.4242 nm) and wood biochar (WB, pore size = 1.6691 nm) were applied to the composting. The results showed that biochar decreased CH4 emissions, mainly through the indirect effect of improving the pile environment. Compared with the control group (CK), the biochars with smaller pore structures, WB and RB, reduced CH4 emissions by 41.83% and 33.59%, respectively, compared to only 8.20% for CB, which has a larger pore structure. In addition, RB and WB increased the free air space (FAS) by more than 10% and CB improved the microbial diversity. Methanothermobacter was reported in WB and RB, with an abundance of 45.45% in WB. Redundancy analysis (RDA) showed that pore size was positively correlated with the CH4 emission rate. The results of this study can provide a theoretical reference for CH4 reduction from biochar co-composting of sewage sludge.

Co-applying biochar and manganese ore can improve the formation and stability of humic acid during co-composting of sewage sludge and corn straw

This study examined the effects of corn straw biochar (CSB) and manganese ore (MO) on the abiotic formation and stability of humic acid (HA) during sewage sludge composting. Co-applying CSB and MO (106%) induced a higher increase in HA content of final compost product than those of no or single applications (32.6–85.1%). This positive change was achieved by promoting the conversion of humus precursors and fulvic acid to HA through abiotic pathway, respectively, in the early and later stages of composting. The co-application of CSB and MO also exhibited a higher capacity to improve HA stability than those of single applications. In sum, this study confirmed a clear synergistic effect of CSB and MO on improving the formation and stability of HA in compost product, which could further enhance the multi-benefits (e.g., carbon sequestration and soil quality improvement) of compost soil application.

Assessment of co-composting of sewage sludge, woodchips, and sawdust: feedstock quality and design and compilation of computational model.

Composting process of sewage sludge requires a preprocessing step in order to prepare the appropriate mixture of dewatered sludge (Xs) with amendment (Xa), bulking agent (Xb), and/or recycled materials (Xr). This research aimed to develop a novel mathematical model for finding an optimal mixture ratio of dewatered sludge with the aforementioned influencing elements on co-composting process. Seven feasible scenarios were presented and the best one was selected in viewpoint of technical and economic perspectives. The optimum mixture was prepared and its quality was evaluated in the terms of physical, chemical, and microbial characteristics. The optimum mixture was loaded in an aerated static pile composting reactor in order to evaluate the quality of the final compost product. If the test results were not in compliance with the USEPA standards, the model was iteratively modified to fulfill the desired objective. The model was validated using the experimental results. The mixture of Xs:Xa:Xb:Xr with a weight ratio 7.4:1.0:1.4:2.3 allowed optimal moisture content (59.8 ± 0.5%), organic matter (80.0 ± 2.6%), dry matter (40.2 ± 0.6%), C/N ratio (28.0 ± 1.6), and free air space (> 30%) across the composting pile. The final product of compost met the heavy metal and microbial requirements for land application. It can be concluded this mathematical model is a promising method for selecting the optimal amount and type of materials for preparing the initial mixture of co-composting process.

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.

Co-composting Versus Direct Ponding of Sewage Sludge on Soil Nutrients Redistribution

Depriving soil fertility serves as one major cause for reduced crop growth rate and production, which in turn affects the food productivity. Various soil conservation measures to sequester the soil nutrients are adopted in developing countries locally and conventionally. In another scenario, present day sewage treatment plants (STP) across the nation are struggling to treat the receiving water quantity effectively. The fluctuations in receiving quantity of waste water resulted in untreated excess sludge dumping in nearby places. In order to synergize the excess sludge dumping in a feasible way by land management practices, the present study aims to compare two methods of sludge incorporating into soil, namely co-composting and direct ponding. Samples were collected from two different plots receiving sludge for different duration (fresh and old) at different depths (12 cm, 24 cm and 36 cm) and analyzed for various physicochemical parameters. The study also highlights the co-composting of sewage sludge with other community wastes to contribute a better analogy on nutrient redistribution. The obtained results of 17.34 mg/l total organic carbon and 1.392 mg/l total nitrogen at 36cm depth in old sludge ponding sites reveals the improved capability of sludge leachate against the soil nutrient attenuation. It finds application in agricultural practice to promote crop growth under controlled conditions of sewage sludge amendment as ponding and co-composting.

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.

Heavy metal accumulation in various tissues of radish (Raphanus sativus) grown under different ratios of organic amendments

Root vegetables have greater risk of metal contamination from compost application to soil than other horticultural crops. Moreover, soil organic amendments pose potential environmental hazards. The objective of the present study was to examine the heavy metal uptake in different tissues (petiole, blade, skin, pulp) of Raphanus sativus exposed to organic amendments doses. The impact of the above materials on heavy metal concentration of the soil and plant development parameters were also evaluated. A pot experiment was established with eight treatments arranged in a randomized complete block design and four replicates. Co-compost of sewage sludge and olive wastes at 100, 200, 300 m3 ha–1, composted olive leaves, olive tree pruning wastes, olive mill pomace and poultry manure at 100, 200 m3 ha–1, commercial liquid organic fertilizer at 50 Kg ha–1 with or without inorganic NPK fertilization and a no fertilizing control, were applied to plants. The results showed that sewage sludge application strongly increased the yield and improved radish size cultivated in silt loam soil. The edible radish part had the lowest Fe, Mn, Cu, Zn, and Cr content, whereas the highest Mn, Cu, Zn, Cr was found in the blade and increased Fe, Ni, Pb were recorded in the skin. Organic treatments gave higher Fe, Mn, Cu, Zn amount in both aerial plant tissues compared to the control soil, while Ni, Pb, Cr of all the radish parts were not affected by treatments. This study suggested that organic amendments application gave low permissible levels of all metal content in radish tissues and increased radish productivity. Therefore, organic materials used herein can be applied for normal plant growth without metal contamination of the plant and the soil.

Effect of Carbon/Nitrogen on Elimination of Coliforms during Composting of Sewage Sludge, Dairy Manure and Sawdust

Composting is a solid waste management alternative to reduce potential hazards in the converting of sewage sludge into reusable material on land. But inefficiency of traditional composting process rate lowers its demand. In-vessel system could provide more effective pathogens reduction and produce pathogen-free soil amendments in comparison with traditional composting systems. In order to achieve successful composting process environmental factors such as temperature, moisture, aeration and nutrients should be sufficiently controlled. This study was undertaken to assess the effect of the carbon/nitrogen (C/N) ratio on reduction or elimination of total and fecal coliforms in co-composting of sewage sludge with dairy manure and sawdust using an in-vessel system under controlled conditions. Temperature, pH and C/N values were used for consideration of the stabilization of the composting process. In this study the minimum temperature of composting process was set to 40 oC by temperature controlled external heater. Initial mesophilic phase occurred within 2 days followed by the thermophilic phase, which lasted for about 10 days. Monitored parameters featured reaction trends to those obtained changes in the mesophilic, thermophilic and maturation phases. A high C/N reduction observed for high initial C/N mixtures (30 and 40) within 7 days of composting. Low initial C/N mixture (20) showed slightly C/N reduction during composting. A higher ratio of C/N preparations led to a higher stabilization rates but higher coliforms reduction achieved with low C/N ratios. Keywords : In-vessel composting, dairy manure, Dewatered sewage sludge, fecal coliforms. DOI : 10.7176/JSTR/5-7-01

Co-composting of sewage sludge and eggplant waste at full scale: Feasibility study to valorize eggplant waste and minimize the odoriferous impact of sewage sludge

Sewage sludge and bulking agent with small proportions of eggplant waste (EP) (4.7 and 8.6%) were co-composted at full scale to evaluate the feasibility of their joint valorization and to reduce the odorous impact during composting. In this sense, physico-chemical, respirometric and olfactometric variables were monitored throughout the co-composting process. The physico-chemical variables studied were related to each other to evaluate their effect on the quality of the final product and the odoriferous impact. It was observed that the reduction in nitrogen concentration was not parallel to the removal of organic matter, which influenced the odor concentration emitted. Furthermore, during the hydrolytic stage of the co-composting process, the odor concentration was lower when the agricultural waste content was highest (8.6% EP: 6317 and 8192 ouE/m3) in comparison with the lowest concentration of EP (4.7% EP: 9214 and 14720 ouE/m3) or without the addition of EP (reference composting pile: 10200 and 22500 ouE/m3). Although sewage sludge is more biodegradable than eggplant waste, the co-composting process was carried out under suitable conditions. Approximately 90 days were required to obtain a stabilized compost. Consequently, co-composting might be a suitable alternative to valorize EP and reduce the odoriferous impact of sewage sludge, with the consequent economic, social and environmental benefits.

Investigation of microbial communities in the field-scale co-composting of sewage sludge and organic municipal solid wastes

The alternative methods should be used to treat sewage sludge and municipal solid wastes which are mostly landfilled in Turkey. Therefore co-composting of these waste streams is a suitable disposal method yielding a useful product. The aim of this study was to investigate the microbial community during the field scale co-composting of sewage sludge and organic municipal solid wastes with addition of bulking agents. Aerated static pile of approximately 26 m3 was used for composting process during 56 days. Investigations of diversity dynamics depending on the temperature were determined by denaturing gradient gel electrophoresis and sequencing of bacterial 16SrDNA-PCR products. The variations of physicochemical parameters and biodegradability during the process were also monitored. The results showed that most of microbial group's role in composting process was temperature dependent and composting was designated by its characteristic thermal profile.

Investigation of microbial communities in the field-scale co-composting of sewage sludge and organic municipal solid wastes

The alternative methods should be used to treat sewage sludge and municipal solid wastes which are mostly landfilled in Turkey. Therefore co-composting of these waste streams is a suitable disposal method yielding a useful product. The aim of this study was to investigate the microbial community during the field scale co-composting of sewage sludge and organic municipal solid wastes with addition of bulking agents. Aerated static pile of approximately 26 m3 was used for composting process during 56 days. Investigations of diversity dynamics depending on the temperature were determined by denaturing gradient gel electrophoresis and sequencing of bacterial 16SrDNA-PCR products. The variations of physicochemical parameters and biodegradability during the process were also monitored. The results showed that most of microbial group's role in composting process was temperature dependent and composting was designated by its characteristic thermal profile.

Addition of wood sawdust during the co-composting of sewage sludge and wheat straw influences seeds germination

The objective of this study was to investigate the effect of addition of sawdust co-composted with sewage sludge and wheat straw on seeds germination. Two mixtures were piled and composted over 90 days. The first mixture (C1) was composed of sewage sludge and wheat straw, while the second mixture (C2) was composed of sewage sludge, wheat straw and wood sawdust. The results showed that the physicochemical parameters of both composts, i.e., temperature (> 55 °C in the thermophilic phase), moisture content (~ 30%). pH (6.73 for C1 and 7.19 for C2) and EC values (1.81 mS cm−1 for C1 and 1.32 mS cm−1 for C2) reached the required maturity standard. The values of C/N were below 12 indicating a high degree of maturity. Also, no bacterial pathogens were detected in the final composts. The concentration of total heavy metals has been reduced allowing the elimination of sewage sludge toxicity, confirmed by the germination index, which reached over 80%. Strong positive correlations were noticed between total Kjeldahl nitrogen of C2 and germination indexes of all the studied species. The obtained results indicate that the addition of wood sawdust increases the nitrogen content leading to slightly alkaline compost which influences seeds germination by reducing the phytotoxicity of sewage sludge.

The effect of FAS and C/N ratios on co-composting of sewage sludge, dairy manure and tomato stalks

This study was conducted to determine the effects of C/N ratio and free air space in co-composting of sewage sludge with tomato stalk and dairy manure. Experiments were carried out in 100 L of stainless steel aerobic compost reactors with full automation system and monitored for 32 days. The temperature was controlled according to the Rutgers strategy. During the composting process, moisture content, organic matter content, pH, electrical conductivity, total carbon, total nitrogen, C/N ratio, total phosphorus, potassium, NH4+-N, NO3--N and heavy metals contents were determined. For evaluation of the stabilization process, organic matter, dry matter, ammonia and mass and volume losses and temperature index values were taken into consideration. The temperature pattern in the mixtures with dairy manure increased rapidly and reached higher levels depending on dairy manure ratio. The highest organic matter loss was 57.87%, which was in the mixture with a C/N ratio of 20 and a free air space ratio of 37%.

Composting of the invasive species Arundo donax with sewage and agri-food sludge: Agronomic, economic and environmental aspects

This work evaluates several co-composting scenarios based on the use of Arundo donax biomass (AD) as bulking agent for the co-composting of sewage sludge (MS) and agri-food sludge (AS), to manage these organic wastes and to produce balanced organic fertilizers by optimizing the process. For this, six piles were prepared in commercial composting conditions, using AD in a range of 40%–80% (on a dry weight basis). Physico-chemical and chemical parameters and the thermal behaviour were evaluated during the process, as were the physical and chemical parameters of the final composts. The proportion of AD in the mixtures has a significant effect on the development of the thermophilic stage of composting, showing the piles with higher proportion of AD a quicker organic matter degradation. In addition, the evolution of the thermal indices R1 and R2 was different depending on the origin of the sludge used, indicating an increase in the relative concentration of more recalcitrant materials in the piles prepared with AS. The estimation of the global warming potential showed that the use of higher proportion of AD in the composting mixture may be a strategy to mitigate the emission of greenhouse gases during the composting process. Moreover, the end-products obtained had an additional marketable value, with a balanced nutrient content and a good degree of maturity, which indicates the viability of the composting process as a method for the stabilization of these organic wastes.

Effect of organic amendment for the construction of favourable urban soils for tree growth

Ornamental tree planting and establishment in cities is a great challenge because urban soil physical properties are unfavourable to the development of root systems. Our objectives were to measure (i) the effects of organic matter on soil physical properties and tree development, and (ii) the effects of ensuing root development on soil physical properties. Using twenty-four 600-L planted or bare soil containers, we monitored physical properties such as dry bulk density, aggregate stability and near-saturated hydraulic conductivity of our reconstituted soils over a 5.5-year period. A 28-cm thick top layer of sandy loam amended with 40% (v/v) sphagnum peat or organic composts was laid on top of a 28-cm thick layer of sandy loam. Bare-root Ostrya carpinifolia trees were planted in half of the 24 containers, and we monitored shoot development and root biomass and distribution. After 5.5 years, trunk diameter had increased from 59 mm for the control soil to 66 mm for soil mixed with green waste compost, and 74 mm for soil mixed with co-compost of sewage sludge and wood chips. After 4.5 years, trunk diameter was strongly correlated with the total number of axes (r = 0.94) and fine root length density (r = 0.98), and was confirmed as a good indicator of tree development. Fine root development increased stable aggregate formation in all treatments as compared to bare soil. After 4.5 years after planting, the tree root system induced by a high organic matter input had significantly improved near-saturated hydraulic conductivity and was fit to support fertile urban soils.

Multivariate relationships between microbial communities and environmental variables during co-composting of sewage sludge and agricultural waste in the presence of PVP-AgNPs

This study evaluated the contributions of environmental variables to the variations in bacterial 16S rDNA, nitrifying and denitrifying genes abundances during composting in the presence of polyvinylpyrrolidone coated silver nanoparticles (PVP-AgNPs). Manual forward selection in redundancy analysis (RDA) indicated that the variation in 16S rDNA was significantly explained by NO3−-N, while nitrifying genes were significantly related with pH, and denitrifying genes were driven by NO3−-N and TN. Partial RDA further revealed that NO3−-N solely explained 28.8% of the variation in 16S rDNA abundance, and pH accounted for 61.8% of the variation in nitrifying genes. NO3−-N and TN accounted for 34.2% and 9.2% of denitrifying genes variation, respectively. The RDA triplots showed that different genes shared different relationships with environmental parameters. Based on these findings, a composting with high efficiency and quality may be conducted in the future work by adjusting the significant environmental variables.