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The behavior of melamine in biological wastewater treatment system
Hongxue An1, Xiaoming Li1, Qi Yang1
1College of Environmental Science and Engineering, Hunan University, Changsha 410082, China; Key Laboratory of Environmental Biology and Pollution Control, Hunan University, Ministry of Education, Changsha 410082, China.
Abstract:
Melamine (MA) is a significant raw material for industry and home furnishing, and an intermediate for pharmacy. However it is also a hazardous material when being added to food as a protein substitute due to the high nitrogen content. In this study, the behavior of MA in activated sludge was investigated. Experiments showed that MA was removed during biological wastewater treatment process, and the removal was mainly achieved by activated sludge adsorption instead of biodegradation. Low levels of MA (0.001-0.10mg/L) in wastewater had negligible influence on the performance of activated sludge, but high levels of MA deteriorated biological nitrogen and phosphorus removal. The presence of MA (1.00 and 5.00mg/L) decreased total nitrogen removal efficiency from 94.15% to 79.47% and 68.04%, respectively. The corresponding concentration of effluent phosphorus increased from 0.11 to 1.45 and 2.06mg/L, respectively. It was also observed that MA inhibited the enzyme activities of nitrite oxidoreductase, nitrate reductase, nitrite reductase and exopolyphosphatase, which were closely relevant to nitrogen and phosphorus removal. Further investigation showed that the presence of high MA concentrations promoted the consumption and synthesis of glycogen, thereby providing the advantage for the growth of glycogen accumulating organisms.
Insights
Melamine (MA) in wastewater is primarily removed by activated sludge adsorption, not biodegradation. High MA levels impair nitrogen and phosphorus removal by inhibiting key enzymes.
Area of Science:
- Environmental Science
- Environmental Chemistry
- Microbiology
Background:
- Melamine (MA) is a crucial industrial chemical with applications in materials and pharmaceuticals.
- MA poses environmental risks when illegally added to food products due to its high nitrogen content.
- Its impact on biological wastewater treatment processes requires thorough investigation.
Purpose of the Study:
- To investigate the behavior and fate of melamine (MA) in activated sludge wastewater treatment.
- To determine the primary removal mechanism of MA in biological treatment systems.
- To assess the effects of varying MA concentrations on activated sludge performance, particularly nitrogen and phosphorus removal.
Main Methods:
- Experimental investigation of MA behavior in activated sludge.
- Analysis of MA removal efficiency and mechanisms (adsorption vs. biodegradation).
- Assessment of MA's impact on nitrogen and phosphorus removal efficiencies and related enzyme activities.
Main Results:
- MA was effectively removed from wastewater, primarily through activated sludge adsorption rather than biodegradation.
- Low MA concentrations (0.001-0.10 mg/L) had minimal impact on activated sludge performance.
- High MA concentrations (1.00 and 5.00 mg/L) significantly reduced nitrogen removal efficiency and increased effluent phosphorus levels.
- MA inhibited key enzymes involved in nitrogen and phosphorus removal, including nitrite oxidoreductase, nitrate reductase, nitrite reductase, and exopolyphosphatase.
- Elevated MA levels promoted glycogen accumulation, favoring the growth of glycogen-accumulating organisms.
Conclusions:
- Activated sludge effectively removes melamine, mainly via adsorption.
- High concentrations of melamine detrimentally affect biological nutrient removal processes by inhibiting essential enzyme activities.
- The findings highlight the potential risks of melamine contamination in wastewater treatment and its impact on effluent quality.
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