Mining Carbon Neutrality Potential in Wastewater Treatment and Resource Recovery from Wastewater

Wastewater management remains a major challenge in developing countries due to the lack of adequate infrastructure, making the need for economically viable and efficient technologies that can be sustained by emerging economies imperative. The upflow anaerobic sludge blanket (UASB) reactor represents an efficient and low-cost technology that produces by-products from which valuable resources can be recovered. This study assessed the energy recovery potential in the form of electricity from biogas and sludge by-products produced by a full-scale UASB reactor. Biogas production rate and composition were monitored to determine the biogas energy recovery potential. Dehydrated sludge from sludge drying beds was likewise quantified and characterised for its elemental composition, immediate composition, gross calorific value and net calorific value to estimate sludge energy recovery potential. The average daily biogas production was found to be 611 ± 275 Nm³/d, with 65% methane in the biogas output. Average sludge dry matter production was determined to be 358.24 TS kg/d. The net energy recovery potential was estimated to be 534.1 MWh/yr, 36% more than the yearly energy demand (392.7 MWh/yr) of the entire plant. Conservative energy recovery at a UASB-based municipal wastewater treatment facility could serve as a self-supply energy option to support its operations. Full article

Residential areas are important for the underlying surface of a city, and the sponge construction of a residential area is a key topic in sponge city construction. Taking the Zi-Jing community as the research case, the SWMM model was established for simulation, and the rainwater runoff control, collection, and utilization were compared and analyzed before and after the implementation of sponge transformation for the designed rainfall conditions of once in 3, 5, 10, 20, and 50 years. The results showed that the water depth of the four outlet pipes was not a full tube at the first peak time. The full duration time was reduced to 1–5 h at the second peak, and the flow reduction rate at the pipe outlet was between 30% and 100%. The water storage of sub-catchments A1, A3, and A4 increased significantly and continued to increase after the peak rainfall occurred, while that of A2 decreased significantly after the transformation after the transformation. For the whole residential area, the surface runoff decreased by 37–47%, while the surface water storage and infiltration increased by 8–14% and 23–39% respectively after reconstruction. The direct storage volume of rainwater in the four sub-catchment areas was filled at least once above a once in 5 years scenario. The main conclusions were as follows: Sponge transformation in residential areas with 17.46% sunken greenbelt and 40.85% permeable pavement, and the time of the pipe outlet in full status can be shortened by 30–200 min in different rainfall return periods. With the increase in the rainfall return period, the improvement range of the infiltration increased from 23.36% to 39.54%, the improvement range of the storage capacity for rainwater decreased from 14.36% to 8.06%, and the reduction degree of surface runoff increased from 37.73% to 47.43%. The water consumption for flushing is about 30 m³ per day for 1000 people, and the rainwater storage volume of 765 m³ in this study can meet the flushing water demand of 5000 residents in the community for 3–5 days. Full article

Ultrasonic treatment is an effective method to disintegrate sludge and extract organic matter and nutrients, including nitrogen and phosphorus, from the sludge. This study investigated the transformation of phosphorus species during the ultrasonic treatment of sludge, to reveal the mechanism of phosphorus migration in the activated sludge structure. The experimental results indicated that power density and ultrasonic time were critical parameters affecting the energy input for sludge integration. The optimal phosphorus release performance was achieved at 2.5 W/mL 10 min. The release of phosphorus showed as a layer-by-layer pattern from the inner sludge core to the outer sphere of the multiple-layer structure of the sludge. The complex sludge structure played an important role in buffering the ultrasonication process and transfer of phosphorus. Mg-P, Ca-P, and organic phosphorus are the main phosphorus species that can be extracted from the sludge core into the supernatant. The three-stage process of phosphorus migration through the sludge layers, including dissolution, reprecipitation, and equilibrium, has been revealed. Full article

Sustainable phosphorus (P) recovery from sewage sludge is crucial to reconciling the simultaneous shortage and excess of P. In this study, magnetic biochar (MBC) was synthesized and innovatively applied to enhance P recovery as vivianite. The effects of anaerobic digestion (AD) time, hydrothermal (HT) pretreatment temperature and MBC dose on vivianite formation were investigated using batch experiments and a modified sequential P extraction protocol. The P fractionation results showed that the concentration of pure vivianite-bound P (Fe(II)-P) reached a maximum on the 10th day of AD treatment, and then declined sharply due to vivianite oxidation and P limitation. HT pretreatment operated at relatively high temperatures (135 and 185 °C) reduced vivianite formation; this negative effect of HT pretreatment was partially compensated by MBC supplementation. The proportion of Fe(II)-P in the solid phase of sludge was substantially raised up to 57.1% from 8.3~17.4% with an increasing dose of MBC from 0 to 12.5 g/L, indicating that MBC had a markedly enhanced effect on vivianite formation; this could be attributed to the MBC-improved Fe(II) production, as evidenced by the elevated proportion of Fe(II) in Fe2p XPS spectra and the increased ratio of Fe(II)-P to oxidized vivianite-bound P (Fe(III)-P) in the sludge after MBC supplementation. MBC addition also decreased the proportion of water-extractable P by sorption and promoted organic P decomposition, which further facilitated vivianite production. These findings reveal a new strategy for enhancing P recovery from HT-pretreated AD sludge. Full article