A DO- and pH-based early warning system of nitrification inhibition for biological nitrogen removal processes

Enhanced nitrogen removal from coal gasification wastewater by simultaneous nitrification and denitrification (SND) in an oxygen-limited aeration sequencing batch biofilm reactor

Simultaneous nitrification and denitrification (SND) for treating coal gasification wastewater (CGW) was achieved successfully in a lab-scale sequencing batch biofilm reactor (SBBR) by oxygen-limited aeration. SND efficiency increased gradually with the concentration of dissolved oxygen (DO) decreased from 4.5mg/L to 0.35mg/L. The maximum SND efficiency of 81.23% was obtained at DO concentration of 0.35mg/L, and the corresponding removal efficiency of NH₄⁺-N and TN reached 76.91% and 70.23%, respectively. Meanwhile, COD was removed significantly and toxic compounds were degraded into biodegradable substances, which relieved effectively the inhibition on nitrogen removal. The results indicated that oxygen-limited condition performed greater toxic compounds and nitrogen removal compared with the aerobic condition. Furthermore, the results of scanning electron microscopic (SEM) and microbial community structure confirmed robust biofilm formation provided a suitable anoxic micro-environment for co-existence of nitrifying and denitrifying bacteria and organics degradation bacteria in the reactor at oxygen-limited condition.

Toxicity measurement in biological wastewater treatment processes: a review

Biological wastewater treatment processes (WWTPs), by nature of their reliance on biological entities to degrade organics and sometimes remove nutrients, are vulnerable to toxicants present in their influent. Various toxicity measurement methods have been adopted for biological WWTPs, but most are performed off-line, and cannot be adapted to on-line monitoring tools to provide an early warning for WWTP operators. However, the past decade has seen a rapid expansion in the research and development of biosensors that can be used for toxicity assessment of aquatic environments. Some of these biosensors have also been shown to be effective for use in biological WWTPs. Nevertheless, more research is needed to: examine the sensitivity of assays and sensors based on single organisms to various toxicants and develop a matrix of biosensors or a biosensor incorporating multiple organisms that can protect WWTPs; test the micro fuel cell (MFC)-based biosensors with real wastewaters and correlate the results with the well-established oxygen uptake rate (OUR)-based or CH4-based toxicity assay; and, develop advanced data processing methods for interpreting the results of on-line toxicity sensors in real WWTPs to reduce the noise due to the normal fluctuation in influent quality and quantity.

Advanced treatment of biologically pretreated coal gasification wastewater using a novel anoxic moving bed biofilm reactor (ANMBBR)-biological aerated filter (BAF) system

A novel system integrating anoxic moving bed biofilm reactor (ANMBBR) and biological aerated filter (BAF) with short-cut biological nitrogen removal (SBNR) process was investigated as advanced treatment of real biologically pretreated coal gasification wastewater (CGW). The results showed the system had efficient capacity of degradation of pollutants especially nitrogen removal. The best performance was obtained at hydraulic residence times of 12h and nitrite recycling ratios of 200%. The removal efficiencies of COD, total organic carbon, NH4(+)-N, total phenols and total nitrogen (TN) were 74.6%, 70.0%, 85.0%, 92.7% and 72.3%, the corresponding effluent concentrations were 35.1, 18.0, 4.8, 2.2 and 13.6mg/L, respectively. Compared with traditional A(2)/O process, the system had high performance of NH4(+)-N and TN removal, especially under the high toxic loading. Moreover, ANMBBR played a key role in eliminating toxicity and degrading refractory compounds, which was beneficial to improve biodegradability of raw wastewater for SBNR process.