Fe-enhanced primary sedimentation and side-stream sludge acidogenesis for efficient nutrient removal, energy-saving and resource recovery in municipal wastewater treatment

Abstract

Conventional wastewater treatment systems are still relying on the core technologies that were developed more than half a century ago, which are no longer capable of accommodating the fast population growth, urbanization and large-scale industrialization in many areas of the world. It is both a grand challenge and a must to develop innovative and more sustainable treatment technologies that are of higher pollutant removal efficiencies, lower energy consumption and capable of energy and resource recovery from wastewater. Major pollutants in municipal wastewater, such as phosphorous (P) and organics, are also valuable materials and resources. However, recovery of such resources is often hindered by their low concentrations in wastewater. This research is proposed to develop an innovative chemical-biological process, namely Fe-enhanced Primary Sedimentation & side-stream Sludge Refinery (Fe-PASSER), for retrofitting and upgrading wastewater treatment systems. The new development is to utilize ferric iron for chemically-enhanced primary treatment (CEPT) to concentrate pollutants (organic and P) into sludge, which also will reduce the pollutant load on the downstream treatment process. An anaerobic reactor is used for the sludge hydrolysis and acidogenesis that transforms settled organic to volatile fatty acids (VFAs) and releases P into the liquid phase for recovery. The VFAs-rich sludge liquor can be used for nitrogen removal by denitrification in wastewater treatment. Moreover, the VFAs may be also used for biosynthesis of polyhydroxyalkanoates (PHAs) as a value-added bioplastic product. The experimental results show that with the Fe-PASSER module the organic and P loads on the downstream biological treatment will be reduced by up to 50% and 70%, respectively, about 50% of P in the wastewater influent can be recovered, VFAs from the side-stream sludge refinery can help increase the nitrogen removal efficiency, and both the power consumption and sludge production in wastewater treatment can be reduced considerably. Moreover, PHAs can be well produced by biosynthesis from the VFAs in the sludge liquor with a PHA yield of about 0.5 g CODPHA/g CODFeed. The novel process can be readily modularized and adopted for upgrading existing treatment facilities to improve the treatment performance, reduce the overall energy consumption and sludge yield and allow effective resource recovery. It is apparent that the new technology will fundamentally transform the current wastewater treatment practice into a more sustainable and resource-mining operation.