As new types of water contaminants continue to emerge, such as retinoids and endocrine-disrupting chemicals, wastewater-treatment techniques are evolving to economically handle them. One new process that has shown promise against both conventional and emerging water pollutants integrates two technologies in tandem — chemically enhanced primary sedimentation (CEPS) of sewage and acidogenic fermentation (AF) of sludge. The process, developed by researchers at University of Hong Kong (HKU; www.hku.hk), is being scaled up at a pilot plant in Shenzhen, China, in collaboration with the Nanshan Sewage Treatment Plant. The pilot plant is currently under construction, and is anticipated to start operations and testing within the next few months. In addition to effective removal of pollutants, the combination of CEPS and AF provides cost benefits in that it enables the recovery of salable materials, including phosphorus and organic compounds.
The CEPS portion of the process utilizes an iron flocculant fed alongside raw wastewater. The resulting sludge sidestream is then fed to an acidogenic membrane bioreactor module for organic hydrolysis (as opposed to digestion, as in a conventional sewage-treatment process). Here, a phosphorus product is recovered, and volatile organic acids are extracted back into the process. In laboratory tests comparing the new process to typical sewage-treatment processes, the combination CEPS-AF system generates cleaner effluent — the team reported that 65–80% of retinoids were removed during the CEPS step, with an additional 50% reduction following the AF step, compared to just 57% reduction using traditional treatment methods. The pilot plant will demonstrate the technology’s potential to be retrofitted into existing treatment plants as an add-on module to further enhance the removal of both conventional and emerging pollutants.
