Life cycle sustainability assessment of advanced treatment techniques for urban wastewater reuse and sewage sludge resource recovery.

Wastewater treatment plants can become a source of valuable resources, such as clean water, energy, fuels and nutrients and thus contribute to the sustainable development goals and a transition to a circular economy. This can be achieved by adopting advanced wastewater and sludge treatment techniques. However, these have to be evaluated on their sustainability to avoid any unintentional consequences. Therefore, this paper presents a life cycle sustainability assessment of advanced wastewater and sludge treatment techniques by integrating the environmental, economic and social aspects. The options considered for advanced wastewater treatment are: i) granular activated carbon; ii) nanofiltration; iii) solar photo-Fenton; and iv) ozonation. The technologies for advanced sludge treatment are: i) agricultural application of anaerobically digested sludge; ii) agricultural application of composted sludge; iii) incineration; iv) pyrolysis; and v) wet air oxidation. The results for the advanced wastewater treatment techniques demonstrate that nanofiltration is the most sustainable option if all the sustainability aspects are considered equally important. If, however, a higher preference is given to the economic aspect, ozonation and granular activated carbon would both be comparable to nanofiltration; if the social aspect is considered more important, only activated carbon would be comparable to nanofiltration. Among the sludge treatment methods, agricultural application of sludge is the most sustainable technique for mean-to-high resource recovery. If the recovery rate is lower, this option is comparable with incineration and pyrolysis with high recovery of their respective products. This work helps to identify the most sustainable techniques that could be combined with conventional wastewater treatments for promoting wastewater reuse and resource recovery across a wide range of operating parameters and products outputs. The findings also support the notion that more sustainable wastewater treatment could be achieved by a circular use of water, energy and nutrients contained in urban wastewaters.

Life cycle environmental impacts of sewage sludge treatment methods for resource recovery considering ecotoxicity of heavy metals and pharmaceutical and personal care products.

Sewage sludge handling is becoming a concern in Europe due to its increasing amount and the presence of contaminants, such as heavy metals and pharmaceutical and personal care products (PPCPs). Currently, over 70% of sludge in Europe is treated thermally by incineration or used as fertilizer in agriculture. New thermochemical methods are under development and are expected to be implemented in the near future. This paper considers the life cycle environmental impacts of the following five alternatives for sludge handling, taking into account the presence of heavy metals and PPCPs: i) agricultural application of anaerobically digested sludge; ii) agricultural application of composted sludge; iii) incineration; iv) pyrolysis; and v) wet air oxidation. The results suggest that anaerobic digestion with recovery of nutrients and electricity has the lowest environmental impacts in 11 out of 18 categories considered. For the mean to maximum resource recovery, composting is the worst alternative, followed by pyrolysis with lower recovery rates. Agricultural application of anaerobically digested sludge has the highest freshwater ecotoxicity due to heavy metals, unless their concentration is in the lowest range, as found in some European sewage sludge applied on land. Therefore, stricter control of heavy metals in the sludge is needed for this option to limit freshwater ecotoxicity to the levels comparable with the thermal processes. The results also indicate that PPCPs have a negligible contribution to freshwater ecotoxicity when compared to heavy metals in the anaerobically digested sludge. Since thermal processes are currently drawing attention due to their potential benefits, the findings of this work suggest that their adoption is environmentally beneficial only if high resource recovery rates can be achieved.

Life cycle assessment of wastewater treatment in developing countries: A review.

Within developing countries, wastewater treatment (WWT) has improved in recent years but remains a high priority sustainability challenge. Accordingly, life cycle assessment (LCA) studies have recently started to analyse the environmental impacts of WWT technologies on the specific context of less developed countries, mainly in China and India. This work presents a comprehensive review of this knowledge with the aim of critically analysing the main conclusions, gaps and challenges for future WWT-related LCAs in developing countries. The most commonly assessed technologies in the 43 reviewed articles are different variations of activated sludge and extensive treatments applied in decentralized systems; however, studies focused on advanced technologies or new sources of pollution (e.g. micropollutants) are still lacking. Goal and system boundaries are normally clearly defined, but significant stages for some technologies such as the construction and sludge management are frequently not included and functional units should be defined accordingly to specific conditions in developing countries. At the inventory level, a more concise description of sources and technical parameters would greatly improve the quality of the LCAs along with accountability of direct greenhouse gas emissions. Eutrophication and global warming are the two most commonly assessed impacts; however, the calculation of terrestrial ecotoxicity when the sludge is used for agricultural purposes, of water use and of the land use change impacts associated to extensive technologies should be encouraged. The estimation of more site-specific databases, characterization factors (especially for eutrophication) or normalization and weighting values combined with more affordable access to background databases and LCA software, would deeply increase the accuracy of WWT-related LCAs in developing countries. An increased usage of the uncertainty analysis should be encouraged to assess the influence of these gaps in the final interpretation of the results. The review finishes with a summary of the main challenges and research gaps identified and with specific guidelines for future researchers to avoid the most common shortcomings found in the reviewed studies.

Environmental assessment of solar photo-Fenton processes in combination with nanofiltration for the removal of micro-contaminants from real wastewaters.

Scarcity of water and concerns about the ecotoxicity of micro-contaminants are driving an interest in the use of advanced tertiary processes in wastewater treatment plants. However, the life cycle environmental implications of these treatments remain uncertain. To address this knowledge gap, this study evaluates through life cycle assessment the following four advanced process options for removal of micro-contaminants from real effluents: i) solar photo-Fenton (SPF) operating at acidic pH; ii) acidic SPF coupled with nanofiltration (NF); iii) SPF operating at neutral pH; and iv) neutral SPF coupled with NF. The results show that acidic SPF coupled with NF is the best option for all 15 impacts considered. For example, its climate change potential is almost three times lower than that of the neutral SPF process (311 vs 928 kg CO2 eq./1000 m3 of treated effluent). The latter is the worst option for 12 impact categories. For the remaining three impacts (acidification, depletion of metals and particulate matter formation), acidic SPF without NF is least sustainable; it is also the second worst option for seven other impacts. Neutral SPF with NF is the second worst technology for climate change, ozone and fossil fuel depletion as well as marine eutrophication. In summary, both types of SPF perform better environmentally with than without NF and the acidic SPF treatment is more sustainable than the neutral version. Thus, the results of this work suggest that ongoing efforts on developing neutral SPF should instead be focused on further improvements of its acidic equivalent coupled with NF. These results can also be used to inform future development of policy related to the removal of micro-contaminants from wastewater.

A methodology for estimating concentrations of pharmaceuticals and personal care products (PPCPs) in wastewater treatment plants and in freshwaters.

Despite an increasing number of studies on pharmaceuticals and personal care products (PPCPs), data on their concentrations in the environment are still scant. This is due to many factors, including great variability in usage and physicochemical properties of these compounds, which contribute to their widespread presence and complex behaviour, particularly in the aquatic environment. The main pathway for their discharge into the waterways is through wastewater treatment plants (WWTPs), which are inefficient in removing many of PPCP compounds. Therefore, aiming to contribute to a better understanding of the role that WWTPs play in the presence of PPCPs in the environment, this paper proposes a new method for estimating the expected concentrations of these compounds in WWTP influents, effluents and sludge, as well as their expected discharge and related concentrations in freshwaters. The proposed method can assist with future eco-toxicological and environmental risk assessments as well as the development of policies and regulation related to PPCP compounds.