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.

In-situ sulfite treatment promotes solid reduction during aerobic digestion of waste activated sludge: Feasibility for small-scale wastewater treatment plants.

Aerobic digestion remains the preferred choice for small-scale wastewater treatment plants (WWTPs) in some developing countries, largely due to economic viability and operational simplicity. The escalating production of waste activated sludge (WAS) has prompted small-scale WWTPs to improve efficiency. To address this issue, this study employed an in-situ sulfite treatment as a non-intrusive method to augment aerobic digestion. With sulfite-enhanced solubilization and hydrolysis, a 3.6-fold increase in degradation was achieved. Both sludge dewatering properties and pathogens inactivation were improved. Microbial community analysis revealed a preferential enrichment of Actinobacteriota and Firmicutes during sulfite treatment. The desktop scaling-up estimation suggests that implementing this treatment yielded operational cost savings exceeding 40 %. In summary, in-situ sulfite treatment offers a cost-effective strategy for WAS management in small-scale WWTPs.

Toward a mechanistic understanding of Rhenium(VII) adsorption behavior onto aminated polymeric adsorbents: Batch experiments, spectroscopic analyses, and theoretical computations.

Rhenium, a rare and critical metal, existing in the industrial wastewater has been aroused extensive interests recently, due to its environmental and resource issues. Chitosan, an easily available, low-cost and eco-friendly biopolymer, was prepared and modified by grafting primary, secondary, tertiary and quaternary amino groups, respectively. Adsorption behaviors and interactions between ReO4- and these four types of aminated adsorbents were investigated through batch experiments, spectroscopic analysis, and theoretical computations. Chitosan modified with secondary amines showed an extremely high uptake of ReO4- with 742.0 mg g-1, which was higher than any reported adsorbents so far. Furthermore, a relatively high adsorption selectivity for Re(VII), as well as the stable and facile regeneration of these aminated adsorbents revealed a promising approach for Re(VII) recovery in full-scale applications. The electrostatic attraction was illustrated to be the main adsorption mechanism by Fourier Transform Infrared Spectroscopy and X-ray Photoelectron Spectroscopy analyses. Significantly, the sub-steps of the adsorption process, encompassing the transformation of binding sites and the subsequent binding between these sites and the adsorbate, have been thoroughly investigated through the density functional theory (DFT) calculation method. This approach was firstly proposed to clearly demonstrate the differences in Re(VII) adsorption behavior onto four types of aminated adsorbents, resulting the importance of not only strong binding energy but also an appropriate binding spatial environmental for effective Re(VII) adsorption.

Achieving efficient methane production from protein-rich organic waste in anaerobic digestion: Using conductive materials or regulating inoculum-to-substrate ratios?

The contribution of inoculum-to-substrate ratios (ISRs) and conductive materials (CMs) on the productivity of anaerobic digestion (AD) remains unclear, particularly for protein-rich organic waste. This study investigated whether the addition of CMs, i.e., biochar and iron powder, can overcome the limitations imposed by varying ISRs for the AD of protein as the sole substrate. Results indicate the ISR plays a decisive role in hydrolysis, acidification, and methanogenesis for protein conversion, irrespective of CMs addition. Methane production increased stepwise as the ISR escalated to 3:1. The addition of CMs provided limited improvement, and iron powder even inhibited methanogenesis at a low ISR. Bacterial community variations were contingent on the ISR, while iron powder supplementation significantly elevates the proportion of hydrogenotrophic methanogen. This study demonstrates that the addition of CMs could affect methanogenic efficiency but can not overcome the limitation of ISRs for the AD of protein.

Achieving superior nitrogen removal in an air-lifting internal circulating reactor for municipal wastewater treatment: Performance, kinetic analysis, and microbial pathways.

Anticipated growth in living standards has accentuated higher requirements for effluent quality from municipal wastewater treatment. In this study, an air-lifting internal circulating reactor with a high internal circulation ratio (36:1) was established to treat municipal wastewater with a long-term operation. In the bioreactor, the average effluent chemical oxygen demand, total nitrogen, and ammonium nitrogen could be 13.1, 5.7, and lower than 1 mg/L, respectively. Further analysis of nitrogen removal showed that traditional nitrification and denitrification, simultaneous nitrification and denitrification (SND), and nitrogen assimilation accounted for 27.4 %, 68.7 %, and 3.9 % respectively. The proportion of aerobic bacteria (Saprospiraceae) and facultative bacteria (Comamonadaceae) were significantly increased, indicating a higher capacity for organic degradation in the reactor. The relative abundance of denitrifying bacteria and bacterial groups with SND (Comamonadaceae) increased. These results suggested the air-lifting internal circulating reactor could be a viable and efficient option for superior nitrogen removal in wastewater treatment.

In-situ sulfite treatment enhanced the production of short-chain fatty acids from waste activated sludge in the side-stream anaerobic fermentation.

Sulfite-based technology could enhance methane production from anaerobic sludge digestion. However, its potential for in-situ direct sludge treatment without anaerobic sludge addition in the side-stream remains unclear. This study investigated the feasibility of using in-situ sulfite treating sludge for short-chain fatty acids (SCFAs) production via anaerobic fermentation of waste activated sludge (WAS) as a side-stream treatment. In-situ sulfite direct sludge treatment enhanced SCFAs and acetic acid production by 2.03 and 4.89 times at 500 mg S/L compared to the control. With in-situ sulfite treatment, WAS hydrolysis and acidification were enhanced while methanogenesis was spontaneously hindered. The in-situ sulfite treatment inactivated pathogens and improved the sludge dewatering properties. The relative abundances of SCFAs-production microbial were stimulated, facilitating the sludge bioconversion. The produced SCFAs from in-situ sulfite side-stream treatment could be applied as an "internal carbon source" to enhance biological nutrient removal to improve economic and environmental value from sludge treatment.

Evaluating Fouling Control and Energy Consumption in a Pilot-Scale, Low-Energy POREFLON Non-Aerated Membrane Bioreactor (LEP-N-MBR) System at Different Frequencies and Amplitudes.

Continual aeration, a fouling control strategy that causes high energy consumption, is the major obstacle in the deployment of membrane bioreactors (MBRs) for wastewater treatment. In recent years, a technology has been developed which adopts mechanical reciprocity for membrane vibration, and it has been proven efficient for membrane scouring, as well as for saving energy: the low-energy POREFLON non-aerated membrane bioreactor (LEP-N-MBR). In this study, a pilot-scale LEP-N-MBR system was designed, established, and operated at various frequencies and amplitudes, and with various membrane models, so as to evaluate energy usage and membrane fouling. The results showed that a slower TMP rise occurred when the frequency and amplitude were set to 0.5 Hz and 10 cm, respectively. Under a suitable frequency and amplitude, the TMP increasing rate of model B (sealed only with epoxy resin) was slower than that of model A (sealed with a combination of polyurethane and epoxy resin). The average specific energy demand (SED) of the LEP-N-MBR was 0.18 kWh·m-3, much lower than the aerated MBR with 0.43 kWh·m-3 (obtained from a previous study), indicating a significant decrease of 59.54% in the SED. However, the uneven distribution of sludge within the membrane tank indicated that the poor hydraulic mixing in the reactor may result in sludge accumulation, which requires further operational optimization. The findings of this pilot-scale study suggest that the LEP-N-MBR system is promising and effective for municipal wastewater treatment with a much lower level of energy usage. More research is needed to further optimize the operation of the LEP-N-MBR for wide application.

Effects of the aeration mode on nitrogen removal in a compact constructed rapid infiltration system for advanced wastewater treatment.

The configuration and the effective operation of constructed rapid infiltration (CRI) systems are of significance for advanced wastewater treatment. In this study, a novel CRI system was developed with a compact structure consisting of two stages, i.e., oxic and anoxic stages. The CRI system was continuously operated for about 140 days under different aeration modes, i.e., tidal flow, continuous aeration, and intermittent aeration. Nitrogen removal was not desirable with tidal flow due to the insufficient oxygen supply in the oxic stage for nitrification, while continuous aeration could achieve good performance for chemical oxygen demand (COD), ammonium, total nitrogen (TN), and total phosphorus (TP) removal. By comparison, the CRI system operated with intermittent aeration was more favorable due to the effective removal ability for pollutants and relatively lower energy demand. The microbial community analysis revealed that Proteobacteria was the dominant phylum in both oxic and anoxic stages of the developed CRI system. Functional microbial groups (Plasticicumulans, Pseudomonas, and Nitrospira in the oxic stage; Thauera, Candidatus_Competibacter, and Dechloromonas in the anoxic stage) were identified for the mediation of carbon, nitrogen, and phosphorus in the system. This study evaluated the feasibility and the optimal aeration mode of the developed CRI system for advanced wastewater treatment, which could satisfy the requirement for the high standard of effluent quality.

Insights into the role of biochar on the acidogenic process and microbial pathways in a granular sulfate-reducing up-flow sludge bed reactor.

In this study, the effect of biochar on sulfate reduction and anaerobic acidogenic process was explored in a granular sulfate-reducing up-flow sludge bed reactor in both long-term operation and batch tests. Both bioreactors had a high sulfate reduction efficiency of over 95% during the long-term operation, while the reactor with biochar addition showed higher sulfate reduction efficiency and stronger robustness against volatile fatty acids accumulation with a higher organic loading and sulfate loading rate. Batch tests showed that adding biochar significantly lessened the lag phase of the sulfate-reducing process, accelerated the adaption of acidogens, and facilitated both production and utilization of volatile fatty acids. The microbial pathways proved that biochar could regulate the acidification fermentation pathway and facilitate the enrichment of assimilative desulfurization bacteria. Overall, this study revealed that the acidogenic sulfate-reducing metabolic pathway could be enhanced by biochar, offering a potential application for effective sulfate-laden wastewater treatment.

"Food waste-wastewater-energy/resource" nexus: Integrating food waste management with wastewater treatment towards urban sustainability.

Sustainable food waste management is a global issue with high priority for improving food security and conserving natural resources and ecosystems. Diverting food waste from the solid waste stream to the wastewater stream is a promising way for food waste source separation, collection, treatment, and disposal. Given the advances in wastewater treatment, this integrated system has great potential for the concurrent recovery of water, resource, and energy. To this end, many efforts from lab-scale to full-scale studies have been devoted to evaluating the feasibility and associated impacts on both solid waste and wastewater systems. This paper summarizes the current status of food waste diversion from the aspects of principle and application. The impacts of food waste diversion on solid waste treatment, sewer system, wastewater treatment, and environmental benefits have been comprehensively reviewed and analysed. In the context of the critical review, this paper further identified the challenges of food waste diversion in unified definitions of the field, sewer network assessment, emerging wastewater treatment technologies, scale-up studies, and policy drivers. Perspectives on the contribution of food waste diversion to a food waste management hierarchy were discussed for initiating the nexus of "food waste-wastewater-energy/resource". We conclude that food waste diversion could facilitate sustainable urban development, but the area-specific factors (e.g., household practices, water resource, sewerage system condition, and treatment techniques) require adequate evaluations to determine the implementation. The outcomes of this study could contribute to the practice and policy-making of food waste management towards urban sustainability.

Revealing the methanogenic pathways for anaerobic digestion of key components in food waste: Performance, microbial community, and implications.

Anaerobic digestion (AD) process is widely considered the most sustainable technology for food waste (FW) disposal due to its advantage of biomethane recovery and beneficial environmental consequences. However, the effects of key components in FW (i.e. starchy food, vegetables, fruits, and meats) on AD process and their methanogenic pathways remain unclear. In this study, the biochemical methane potential (BMP) of cooked rice, cabbage, banana peel, pork and local FW was 288, 283, 254, 630, and 476 NmL CH4/g VSadded, with t80 (time required for 80% methane produced) of 3, 9, 3, 11 and 11 days, respectively. Kinetic analysis suggested diverse hydrolysis rates (0.104-0.679 d-1) and specific methane yields (39-119 NmL CH4/g VSadded/d). The relative abundances of key methanogens in the reactors were diverse, leading to the variation in acetoclastic and hydrogenotrophic methanogenic pathways. This study provides fundamental information for the operation of AD systems with different FW compositions.

Integrating sulfur, iron(II), and fixed organic carbon for mixotrophic denitrification in a composite filter bed reactor for decentralized wastewater treatment: Performance and microbial community.

Decentralized wastewater treatment in rural areas is an imperative challenge around the world, particularly in developing countries. The composite filter bed reactor is viable for decentralized wastewater treatment, but its performance on nitrogen removal often fluctuates with the unstable influent characteristics and loadings. Here, a composite filter bed reactor integrating sulfur, iron(II), and fixed organic carbon (shaddock peel) was developed and continuously operated under different conditions. The fixed organic carbon source promoted nitrogen removal with an efficiency higher than 90% and reduced effluent sulfate level by 40%, indicating that the integrated electron donors could improve the resistance and stability of the reactor. Moreover, sulfur-oxidizing bacteria (Thiomonas, Sulfuriferula, and Acidithiobacillus), iron-oxidizing bacteria (Ferritrophicum), and denitrifiers (Simplicispira and Hydrogenophaga) were identified in the anoxic/anaerobic layer of the reactor, suggesting that mixotrophic denitrification was stimulated by sulfur, iron(II), and fixed organic carbon. The findings of this study indicate that the developed reactor with the integrated electron donors could be reliable for carbon, nitrogen, and phosphorus removal and promising for the application of decentralized wastewater treatment.

Phosphate sequestration by magnetic La-impregnated bentonite granules: A combined experimental and DFT study.

To use the lanthanum hydroxide (La(OH)3) as a low-cost, highly-efficient, and recyclable adsorbent, it could be embedded on a magnetic substance to improve its physical features and lower the overall cost. Herein, novel millimetric-size magnetic lanthanum-modified bentonite (La-MB) granules were fabricated for P sequestration, and the adsorption performance and mechanisms were systematic studied. The maximum capacity of P uptake by La-MB was up to 48.4 mg/g, which was higher than many previous reported La-based adsorbents. Moreover, the enhanced uptake of P was achieved over a wide pH range (3-9) and in the coexistence of common anions (Cl-, NO3-, and SO42-). Besides, the exhausted La-MB can be effectively regenerated by 5 mol/L NaOH with about 94.5% desorption efficiency and 60.8% uptake capacity remained during 5 cycles. The La-MB also exhibited excellent performance of anti-interference in two kinds of real wastewaters. The postsorption characterization and DFT calculations revealed that the electrostatic interaction and chemical precipitation jointly facilitated phosphate sequestration by La-MB during the rapid sorption phase, while ligand exchange and complexation reaction played more important roles than others during the slow sorption step. The electrostatic interaction not only effectively promoted the ligand exchange, and also further accelerated chemical precipitation via the formation of LaPO4 during the whole process of phosphate uptake. Overall, millimetric La-MB is considered to have great potential for engineering application, and this work also provides new insights into the molecular-level mechanism of phosphate sequestration by La-MB.

Catalytic oxidation of diclofenac by hydroxylamine-enhanced Cu nanoparticles and the efficient neutral heterogeneous-homogeneous reactive copper cycle.

This study has demonstrated that hydroxylamine (HA) could greatly enhance Cu nanoparticles (nCu) in activating molecular oxygen and significantly elevate the diclofenac (DCF) degradation rate about two orders of magnitude in neutral circumstances. Effects of several important parameters on the DCF degradation such as nCu loading, HA dosage, pH and reaction temperature were investigated in the nCu/HA/O2 system. Multiple examinations revealed that the reactive Cu(III) species instead of OH• would be predominant in the nCu/HA/O2 system, despite their similar DCF degradation pathways. Based on a HA-enhanced copper cycle depending on the pristine Cu0@Cu(I) (hydro)oxides core-shell structure, the heterogeneous-homogeneous reaction mechanism was proposed. It included solid-liquid interfacial and bulk reactions, e.g. heterogeneous activation of O2 by Cu(I) to produce H2O2 and homogeneous Cu(I)-catalytic generation of Cu(III) from H2O2. Further quantitative investigation of the main reactive species in the cycle revealed that the Cu(I) regeneration instead of the O2 activation would be rate-limited. Besides, nCu could be recycled to effectively degrade DCF in four consecutive cycles in the raw neural nCu/HA/O2 system. It suggested that the nCu/HA/O2 system with a more efficient copper cycle would be a good alternative Fenton-like system in treating neutral recalcitrant organic wastewaters.

Enhanced phosphate sequestration by Fe(iii) modified biochar derived from coconut shell.

In this work, a novel Fe-modified coconut shell biochar (Fe-CSB) was synthesized and utilized to remove phosphate from aqueous solution. Characterization results confirmed that the iron in the Fe(iii)-impregnated CSB existed mainly in the amorphous phase, as ferrihydrite and amorphous hydroxide, which substantially enhanced the phosphate adsorption. Batch experiments indicated that phosphate adsorption on the Fe-CSB was highly dependent on the pH, the humic acid, and temperature, while it was less affected by the nitrate. Phosphate adsorption by the CSB and Fe-CSB could be well described by the pseudo n-th order and Langmuir-Freundlich models. The fitting of the experimental data with the intra-particle diffusion model revealed that surface adsorption and inner-sphere diffusion were involved in the phosphate adsorption process, and that the latter was the rate-controlling step. Batch adsorption experiments and post-adsorption characterization results revealed that the phosphate adsorption by Fe-CSB was primarily governed by four mechanisms: ligand exchange, electrostatic attraction, chemical precipitation, and inner-sphere complexation. This work demonstrated that the modified Fe-CSB is an environmentally friendly and cost-effective bioretention medium and could open up new pathways for the removal of phosphorus from stormwater, as well as solve the problem of waste biomass pollution.