Comparison on the Treatment Performance of Full-scale Sewage Treatment Plants using Conventional and Modified Activated Sludge Processes

摘要

The objective of the study is to identify and carry out studies on the selected five (5) existing sewage treatment plants (STPs) in terms of their treatment performance. The five selected sewage treatment plants have different treatment processes, a) Sequencing Batch Reactor (SBR) b) Modified Oxidation Ditch (MOD) c) Advanced Oxidation Ditch (AOD) d) Advanced Conventional Activated Sludge System (ACAS) and e) Extended Aeration (EA) types. Assessment on the removal efficiency and sludge quality of the major pollutant parameters namely BOD, COD, TSS, O&G NH_3-N, PO_4 of the effluent and heavy metals content of sludge were carried out based on the sampling done by an accredited laboratory. The health of the aeration tanks was also investigated. On average COD recorded highest removal for all STPs at 91% followed by TSS (88%), O&G (86%), BOD (84%) and PO_4 (71%). The removal of NH_3-N was low, at only 72%; with a big range of removal rate between the highest of 97% for SBR type and only 17% removal for the EA type. Comparison with other sludge approved for use in agriculture as well as compost standards showed that the heavy metals contents of raw sludges comply with those approved for sewage sludges for agriculture, as can be found in the USA, Australia and Spain. Comparison with levels limited by the UK Composting Association Quality (CAQ) and European EC Compost Ecolabel (ECCE) shows that the raw sludge levels exceed most of the ECCE's levels.