Advanced wastewater treatment systems

Abstract

Technical progress in the field of municipal wastewater treatment, which includes removal of eutrophicating pollution loads, has in the past few years significantly improved the process flow of sewage treatment plants. More attention is now being paid to the high number of disease-causing germs in the sewage treatment plant effluent. Micro and ultra filtration, combined with the activated sludge process, has turned out in recent years to be a suitable method for minimising the effluent load. Tightening discharge standards for sewage treatment effluents can thus be met, without the need for the conventional aeration and secondary clarification tanks or filtration and disinfection plants. Membrane bioreactor technology provides a good alternative to the conventional treatment of municipal wastewater (Huber Technology, 2004). - Most of the current regulatory requirements will be met by the membrane separation step. - Membrane bioreactor technology is a space saving technique. Its modulebased design allows the capacity to be easily increased when needed. - Membranes will continue to decrease in price in the coming years. - With improved effluent quality, re-use of the formerly wasted effluent is possible, which makes it a sustainable technology. - It combines the biological treatment with a membrane separation step. Because of this combination it has several advantages over conventional treatment by activated sludge followed by a settling tank. - The settling tank is unnecessary because of the membrane separation; submerged membrane bioreactors can be up to 5 times smaller than a conventional activated sludge plant. - Membrane bioreactors can be operated at mixed liquor suspended solids of up to 20,000 mg/L. - Biomass concentration can be greater than in conventional systems, which reduces reactor volume. - The membrane can retain soluble material with a high molecular weight, improving its biodegradation in the bioreactor. - Good effluent quality. - Good disinfection capability, with significant bacterial and viral reductions achievable using UF and MF membranes. This paper describes the activated sludge treatment and the membrane bioreactor processes, using Melbourne Water's Western Treatment plant at Werribee, in Victoria, and CitiWater's Magnetic Island plant, in Queensland, as examples of the treatment processes. Sufficient information is given to permit an understanding of the two processes and their relationships. The more recent MBR technology can be seen as an emulation of the natural filtration processes occurring in broad acre treatment, without the large tracts of land area, or the plant and the number of required processes needed for later advancements.