Application of ceramic Ultrafiltration/Reverse Osmosis membranes and enhanced membrane bioreactor for the reuse of car wash wastewater

摘要

The most convenient way of transportation is car and the use of car is increasing to improve our daily activities. According to the Motor Vehicle Census (MVC) in 2016, there are 18.4 million registered motor vehicles in Australia. The demand of car washing is also increasing for better maintenance of these cars. But the wastewater generated from this car wash centers is a major concern for the environment as it contains different type of pollutants such as petroleum hydrocarbon waste (gasoline, diesel and motor oil), heavy metals (such as copper, lead and zinc), nutrients (phosphorus and nitrogen), surfactants and suspended solids, microorganisms, sand and dust. A literature survey showed that over 35 billion litres of contaminated wastewater are being disposed of rather than recycled from 10,000 car wash centers in Australia every year. Therefore, appropriate treatment processes are required to treat car wash wastewater which enables us to reuse the treated water at car wash facilities and efficiently isolate pollutants from the wastewater. Past research studies have used different treatment technology comprising of conventional treatment and membrane based treatment. The aim of this study is to develop a treatment system which is cost effective, have a small footprint (with respect to space) and produce high-quality recycled water. After critically evaluating the available literature and previous studies, two membrane based technologies were selected here. The first treatment system comprising of coagulation-flocculation, sand filtration, ceramic ultrafiltration membrane and reverse osmosis were set-up in the Laboratory, and the treated water qualities were analyzed to evaluate the removal efficiency of various parameters at every step. An Enhanced Membrane Bioreactor (eMBR) was selected as a second treatment system in this research. The eMBR system comprised of anaerobic and anoxic bioreactors followed by an aerobic membrane bioreactor as well as an ultraviolet (UV) disinfection unit which are a combination of biological treatment, membrane separation, and physical treatment processes. This treatment systems were set-up in the laboratory and ran for 17 months. In the first stage of experiment, synthetic wastewater was used to acclimatize the microorganisms present in all three reactors (anaerobic, anoxic and aerobic membrane bioreactor). In the second stage, different percentage of car wash wastewater was introduced with the synthetic wastewater. The permeate water quality was analyzed to evaluate the removal efficiency of various parameters. The short term critical flux tests were conducted to determine the fouling characteristics of the membrane. In the final stage, the hydraulic retention time (HRT) of the system was reduced to find out the optimum operating condition. Moreover, the performances of the first and second treatment systems were compared based on the recycled water quality. It was found from the experimental results that both treatment systems were able to produce high-quality recycled water which can be reused for washing the cars in a car wash center. However, eMBR was able to produce higher-quality permeate compare to first treatment system (in the first treatment system the removal efficiencies of COD, turbidity and total nitrogen were 96.1, 99.9 and 74.4%, respectively and in the eMBR they were 99.6, 99.9 and 66.3%, respectively). Moreover, first treatment system produced a significant amount of waste whereas eMBR produced no disposable waste during 17 months of operation.