Abstract
This study applied a multi-level contact oxidation process system in a pilot-scale experiment to treat automobile painting wastewater. The experimental wastewater had been pre-treated through a series of physicochemical methods, but the water still contained a high concentration of chemical oxygen demand (COD) and had poor biodegradability. After the biological treatment, the COD concentration of effluent could stay below 300 mg/L. The study analyzed the effects of hydraulic residence time (HRT) on COD, ammonia nitrogen (NH4+-N), and total nitrogen (TN). The optimal HRT was 8 h; at that time, removal efficiencies of COD, ammonia nitrogen, and total nitrogen were 83.8%, 86.3%, and 65%, respectively. The system also greatly reduced excess sludge production; the removal efficiency was 82.8% with a HRT of 8 h. The study applied high-throughput pyrosequencing technology to evaluate the microbial diversity and community structures in distinct stages of the biological reactor. The relevance between process performance and microbial community structure was analyzed at the phylum and class level. The abundant Firmicutes made a large contribution to improving the biodegradability of painting wastewater through hydrolysis acidification and reducing sludge production through fermentation in the biological reactor.
Highlights
The automobile industry has rapidly developed, prompting significant interest in automobile painting wastewater treatment
Since a number of chemical materials are applied during these processes, the wastewater is characterized by high concentrations of organics, heavy metal, suspended solids, as well as a low biodegradability index, which is extremely hazardous in environment [1]
The process performance indicated that this biological system could efficiently degrade the remaining refractory performance indicated that this biological system could efficiently degrade the remaining refractory organic substances in painting wastewater
Summary
The automobile industry has rapidly developed, prompting significant interest in automobile painting wastewater treatment. Automobile painting processes generate different kinds of wastewater, from activities such as degreasing, activation, passivation, electrophoresis, acid cleaning, and alkaline cleaning. Since a number of chemical materials are applied during these processes, the wastewater is characterized by high concentrations of organics, heavy metal, suspended solids, as well as a low biodegradability index, which is extremely hazardous in environment [1]. The concentration of automobile painting wastewater varies widely, and is decided by many factors, like discharge cycles, production and cleaning process, types of chemical used, etc. The typical characteristics of automobile painting wastewater are as follows: pH is in the range of between 6 and 12, chemical oxygen demand (COD) is 1400–5900 mg/L, Water 2017, 9, 881; doi:10.3390/w9110881 www.mdpi.com/journal/water
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