Sustainability analysis of implementing sludge reduction in overall sludge management process: Where do we stand?

Comparative life cycle assessment of sewage sludge treatment in Wuhan, China: Sustainability evaluation and potential implications

Owing to the relentless growth of sewage sludge production, achieving low-carbon development in sewage sludge treatment and disposal (STD) is becoming increasingly challenging and unpredictable. However, the STD varied spatially, and city-specific analysis is deemed necessary for sustainable evaluation. Therefore, a lifecycle-based greenhouse gas (GHG), energy, and economic analysis were conducted by considering six local STD alternatives in Wuhan City, China, as a case study. The findings indicated anaerobic digestion combined with digestate utilization for urban greening (ADL) and incineration in existing power plants (INCP) exhibited the least GHG emissions at 34.073 kg CO2 eq/FU and 644.128 kg CO2 eq/FU, while INCP generated the most energy at -2594 kW.h/FU. The economic evaluation revealed that ADL and INCP were more beneficial without accounting for land acquisition. Scenario analysis showed that the energy recovery from ADL and INCP is significantly influenced by the hydrolysis yielding rate and sludge organic content. Perturbation sensitivity indicates that regional emission factor of electricity and electricity fee highly influence the overall GHG emission and cost. The results of this study could assist policymakers in identifying viable solutions to the cities experiencing the same sludge treatment burdens.

Life cycle assessment of nutrient recovery strategies from domestic wastewaters to quantify environmental performance and identification of trade-offs

Increase in anthropogenic activities proliferated the consumption of resources such as phosphorus; and increase the adverse environmental impacts especially eutrophication on water resources such as lakes. Nutrient recovery from domestic wastewaters to produce a fertiliser has been explored to address these challenges in the context of a sustainable circular nutrient economy. Life cycle assessment (LCA) was performed to holistically assess the impacts of integrating a nutrient recovery system on wastewater and water resource management using Laguna de Bay, Philippines as the geographical boundary. The inventory was developed based on the results of the emerging nutrient recovery reactor operations and the application of the recovered fertiliser on the agricultural crops. The LCA results for the proposed scenario showed environmental benefits of about 83.6% freshwater eutrophication, 102.5% terrestrial ecotoxicity, 26.9% water consumption, 100.7% mineral resource scarcity, while the global warming potential is 95.4% higher than the baseline scenario. Results imply policy review for septage management, system optimisation, and evaluation of alternative methods of wastewater management, in terms of life cycle thinking and sustainability across the globe.

Life cycle environmental benefits of recycling waste liquor and chemicals in production of lignocellulosic bioethanol

In recent decades, numerous bioconversion processes and techniques have been developed to utilize lignocellulosic biomass as feedstock in the production of bio-based fuels and materials. However, waste treatment, an important sub-system, is seldom considered in the life cycle assessment of lignocellulose derived products. This study comprehensively investigated the environmental impacts of bioethanol and electricity cogeneration from sugarcane bagasse, with a focus on recycling techniques adopted in waste treatment. A life cycle assessment indicated that high recycle rate of black liquor, acid and waste washing water can substantially reduce the consumption of fresh water, related chemicals and energy by 70-80%. Environmental impacts relating to global warming, acidification potential and primary energy demand can be decreased by 5-10 times or even entirely eliminated. These study outcomes demonstrate significant environmental benefits of integrating waste recycling techniques into lignocellulose biorefinery process, providing a solid foundation for future industrial development.

The efficiency and mechanism of excess sludge-based biochar catalyst in catalytic ozonation of landfill leachate

In this study, biochar was produced based on dehydrated excess sludge from the municipal wastewater treatment plant, which was used for catalytic ozonation of pollutants derived from landfill leachate. The necessary catalytic sites in the structure of biochar were originated from the inorganic metals and organic matters in the sludge, which included a large number of functional groups (e.g., C-C, CO, etc.), adsorbed oxygen (Oads accounted for 44.82%) and electron defects (ID/IG=1.01). These active sites could promote the generation of reactive oxygen species (ROS) (e.g., ·OH,·O2-, etc.). The synergistic interaction between the microorganisms in the activated sludge also facilitated the removal rates of pollutants. Proteobacteria, Bacteroidetes, and Deinococcu-Thermus were crucial in the bioreactor. In 16 days of reaction, the removal ratios of NH+4-N and COD were 98.95 ± 0.11% and 90.89 ± 0.47%, respectively. This study not only explains the mechanism of catalytic ozonation of biochar, but also provides a new way of the practical treatment of landfill leachate.

A comprehensive assessment on sludge conditioning by pyrite acid eluent-activated peroxymonosulfate based on dewaterability, heavy metals risk and ore recovery

Wastewater activated sludge (WAS) has poor dewaterability and contains heavy metals (HMs), limiting its land application. Therefore, in this study, a novel pyrite acid eluent-activated peroxymonosulfate (Fe2+pyrite/PMS) conditioning approach that can completely recover the residual pyrite and greatly reduce acid use was developed to improve WAS dewaterability, and the HMs chemical speciation and risks of conditioned WAS were assessed. Our results showed that under the optimized operational parameters, the capillary suction time (CST) and water content (Wc) of WAS decreased by 46.03% and 7.75%, respectively. Furthermore, during Fe2+pyrite/PMS conditioning processing, sulfate radical (SO4-) destroyed the extracellular polymeric substances (EPS) matrix, causing bound water release and the decrease of proteins/polysaccharides in outer layered EPS, even the decomposition of some protein-N in tightly bound EPS (TB-EPS) into inorganic-N. In addition, although the total concentration of HMs in the conditioned WAS matrix increased, the Ni concentration decreased in the solid fraction. Further, the risk assessment code (RAC) levels did not increase, and the eco-toxicity of Cr became weakened after Fe2+pyrite/PMS conditioning. However, after acid extraction, the pyrite residue had worsened recycle performance because the passivation layer contained S0/Sn2- on its surface, and no additional elements were detected in the pyrite residue, which had almost no effect on its further usage.

Changes in microbial community during hydrolyzed sludge reduction

In this study, the effects of different enzymes (lysozyme, α-amylase and neutral protease) on sludge hydrolysis efficiency and microbial community in sequencing batch reactor (SBR) were introduced. The results showed that the hydrolysis efficiencies of the three enzymes were 48.5, 22.5 and 31%, respectively, compared with the accumulated sludge discharge of the blank control group. However, it has varying degrees of impact on the effluent quality, and the denitrification and phosphorus removal effect of the system deteriorates. The lysozyme that achieves the optimal sludge hydrolysis effect of 48.5% has the greatest impact on the chemical oxygen demand (COD), total nitrogen (TN), and nitrate nitrogen (NO3--N) of the effluent. The sludge samples of the control group and the groups supplemented with different enzyme preparations were subjected to high-throughput sequencing. It was found that the number of OTUs (Operational Taxonomic Units) of the samples was lysozyme > α-amylase > blank control > neutral protease. Moreover, the abundance grade curve of the sludge samples supplemented with lysozyme and α-amylase was smoother, and the community richness and diversity were improved by lysozyme and α-amylase. The species diversity of the sludge supplemented with lysozyme and neutral protease was great, and the community succession was obvious. The introduction of enzymes did not change the main microbial communities of the sludge, which were mainly Proteobacteria, Actinobacteria and Bacteroidetes. The effects of three enzyme preparations on sludge reduction and microbial diversity during pilot operation were analyzed, the gap in microbial research was filled, which provided theoretical value for the practical operation of enzymatic sludge reduction.