Sludge incineration and seawater desalination are two approaches that can be used in the disposal of waste activated sludge (WAS) and for obtaining fresh water. As resource recovery from wastewater treatment and water purification is a topic of particular interest in these times, “water mining” has become a focus of research, with phosphate/P-recovery from WAS incineration ash, and extraction of useful elements from the brine of desalination being important steps in the pursuit of a circular/blue economy. However, P-recovery from ash involves removing metals, which need to be disposed of carefully, as does the brine collected. If cations in the ash and anions in the brine could be combined in order to produce coagulants/flocculants, a new circular model would be established. A preliminary experiment for this purpose has demonstrated that a liquid poly‑aluminum chloride (PAC) could be synthesized from the aluminum ion/Al3+ removed from the ash and the original brine. With this work, we synthesized the liquid PAC by a hydrothermal method, and the results from infrared spectrometer demonstrated that the synthesized PAC was similar to a commercial PAC. Moreover, the synthesized PAC was able to efficiently reduce the effluent turbidity of wastewater treatment plants (WWTPs), especially when compared with the commercial PAC. It is therefore important that research in this area be continued in order to improve the quality of synthesized coagulants and to produce different coagulants based on cations and anions in ash and brine.@en

Wet-chemical approach is widely applied for phosphate recovery from incinerated ash of waste activated sludge (WAS), along with metals removed/recovered. The high contents of both aluminum (Al) and iron (Fe) in WAS-incinerated ash should be suitable for producing coagulants with some waste anions like Cl− and SO42− With acid (HCl) leaching and metals’ removing, approximately 88 wt% of phosphorus (P) in the ash could be recovered as hydroxylapatite (HAP: Ca5(PO4)3OH); Fe3+ in the acidic leachate could be selectively removed/recovered by extraction with an organic solvent of tributyl phosphate (TBP), and thus a FeCl3-based coagulant could be synthesized by stripping the raffinate with the original brine (containing abundant Cl− and SO42−). Furthermore, a liquid poly-aluminum chloride (PAC)-based coagulant could also be synthesized with Al3+ removed from the ash and the brine, which behaved almost the same in the coagulation performance as a commercial coagulant on both phosphate and turbidity removals. Both P-recovery from the ash and coagulant production associated with the brine would enlarge the markets of both ‘blue’ phosphate and ‘green’ coagulants.@en

Conventional wastewater treatment plants (WWTPs) clean wastewater and minimize water pollution; but, while doing so, they also contribute to air pollution and need energy/material input with associated emissions. However, energy recovery (e.g. anaerobic digestion) and resource recovery (e.g. water reuse) allow us to offset the adverse environmental impacts of wastewater treatment. Life cycle assessments (LCA) have been used more and more to evaluate the environmental impacts of WWTPs and to suggest improvement options. There is a need to search for resource recovery applications that genuinely realize a net-zero impact on the total environment of WWTPs. In this work, a scheme with highly efficient energy and resource recovery (especially for thermal energy) is proposed and evaluated. The environmental impact of a conventional WWTP in comparison with the scheme proposed here, with energy/resource recovery included, was calculated, and discussed with reference to LCA methodology. In the process of using LCA, it was necessary to choose a regional situation to focus on. In this case, a Chinese situation was focused as a reference, but the qualitative information gained is of worldwide relevance. The results clearly revealed that conventional WWTP does not benefit the total environment as a whole while the new scheme benefited the total environment via resource/energy recovery-based processes. Among others, thermal energy recovery played a significant role towards a net-zero LCA analysis (contributing around 40%) which suggests that more attention and research should be focused on it.@en

Conventional wastewater treatment plants (WWTPs) clean wastewater and minimize water pollution; but, while doing so, they also contribute to air pollution and need energy/material input with associated emissions. However, energy recovery (e.g. anaerobic digestion) and resource recovery (e.g. water reuse) allow us to offset the adverse environmental impacts of wastewater treatment. Life cycle assessments (LCA) have been used more and more to evaluate the environmental impacts of WWTPs and to suggest improvement options. There is a need to search for resource recovery applications that genuinely realize a net-zero impact on the total environment of WWTPs. In this work, a scheme with highly efficient energy and resource recovery (especially for thermal energy) is proposed and evaluated. The environmental impact of a conventional WWTP in comparison with the scheme proposed here, with energy/resource recovery included, was calculated, and discussed with reference to LCA methodology. In the process of using LCA, it was necessary to choose a regional situation to focus on. In this case, a Chinese situation was focused as a reference, but the qualitative information gained is of worldwide relevance. The results clearly revealed that conventional WWTP does not benefit the total environment as a whole while the new scheme benefited the total environment via resource/energy recovery-based processes. Among others, thermal energy recovery played a significant role towards a net-zero LCA analysis (contributing around 40%) which suggests that more attention and research should be focused on it.@en

地下式污水处理厂建设近年在我国兴起，且有扩展之势。地下污水厂地表可形成的景观环境直观、易觉，这就使污水处理厂可与景观环境建设合二为一的说法盛行。反观更加缺地的欧洲、日本等地，地下式污水处理厂其实并不多见，让人不免心生疑窦。因此，有必要通过一些方法对地下式污水处理厂进行综合影响评价，以揭示其综合效益之优劣。以国内某全地下式污水处理厂为研究实例，并以相同工艺的地上式污水处理厂作为对比参照物，通过全生命周期环境影响评价（LCIA）、全生命周期成本（LCC）评价及全生命周期生态效益（LCEE）评价3种方法分别对地下式污水处理厂进行全方位影响评价，最后将3种评价结果归一化为全生命周期综合影响（LCCI）评价。综合影响评价结果显示，地下式污水处理厂在环境影响、基建投资、生态效益三方面的综合负面影响较地上式要高出约20%。虽然地下式污水处理厂地表园林景观会产生一定生态效益，但这并不能“中和”其环境影响以及基建投资所产生的负面效益。因此，地下式污水处理厂建设并非优选方式，需要因地制宜，选址要特别慎重。 Abstract: Constructing underground wastewater treatment plants (UWWTPs) prevails recently and tends to extend largely in China. Ecological landscape saved by UWWTPs is easy to be seen, which makes an opinion popular that wastewater treatment could combined with ecological landscape. In Europe and Japan much shorter of land, however, it is rare to see UWWTPs, which makes us a query. Therefore, it is necessary to comprehensively assess UWWTPs in some ways and to reveal their pluses and minuses. Based on life cycle impact assessment (LCIA), life cycle cost (LCC) assessment and life cycle ecological efficiency (LCEE) assessment, the study assessed omnibearingly the impacts and efficiencies of UWWTPs, and finally the assessed results from each assessment were normalized into life cycle comprehensive impact (LCCI) assessment. The assessment was based on a real domestic UWWTP, and a proposed surface WWTP was used as a counterpart for comparison. The LCCI results revealed that the comprehensively negative efficiency of UWWTP on the environment, infrastructure investment and ecological efficiency was about 20% higher than that of its counterpart. Although the ecological landscape restored by the UWWTP could form a certain ecological efficiency, it could not neutralize the negative efficiency of the UWWTP on the environment and the infrastructure investment. As a result, UWWTPs are not a preference approach to municipal wastewater treatment. So constructing UWWTP should act according to circumstances and selecting sites of UWWTP have to be prudent.@en