[Show abstract][Hide abstract] ABSTRACT: Moving bed biofilm reactor (MBBR) was used to treat real coal gasification wastewater. Nitrification of the MBBR was inhibited almost completely during start-up period. Sudden increase of influent total NH3 concentration was the main factor inducing nitrification inhibition. Increasing DO concentration in the bulk liquid (from 2 to 3 mg/L) had little effect on nitrification recovery. Nitrification of the MBBR recovered partially by the addition of nitrifying sludge into the reactor and almost ceased within 5 days. Nitrification ratio of the MBBR achieved 65% within 12 days by increasing dilute ratio of the influent wastewater with tap water. The ratio of nitrification decreased to 25% when influent COD concentration increased from 650 to 1000 mg/L after nitrification recovery and recovered 70% for another 4 days.
[Show abstract][Hide abstract] ABSTRACT: Lurgi coal gasification wastewater (LCGW) is a refractory wastewater, whose anaerobic treatment has been a severe problem due to its toxicity and poor biodegradability. Using a mesophilic (35±2°C) reactor as a control, thermophilic anaerobic digestion (55±2°C) of LCGW was investigated in a UASB reactor. After 120 days of operation, the removal of COD and total phenols by the thermophilic reactor could reach 50-55% and 50-60% respectively, at an organic loading rate of 2.5 kg COD/(m(3) d) and HRT of 24 h; the corresponding efficiencies were both only 20-30% in the mesophilic reactor. After thermophilic digestion, the wastewater concentrations of the aerobic effluent COD could reach below 200 mg/L compared with around 294 mg/L if mesophilic digestion was done and around 375 mg/L if sole aerobic pretreatment was done. The results suggested that thermophilic anaerobic digestion improved significantly both anaerobic and aerobic biodegradation of LCGW.
[Show abstract][Hide abstract] ABSTRACT: Coal gasification effluent is a typical refractory industrial wastewater with a very poor anaerobic biodegradability due to its toxicity. Methanol was introduced to improve anaerobic biodegradability of real coal gasification wastewater, and the effect of methanol addition on the performance was investigated in a mesophilic upflow anaerobic sludge bed reactor with a hydraulic retention time of 24 hr. Experimental results indicated that anaerobic treatment of coal gasification wastewater was feasible with the addition of methanol. The corresponding maximum COD and phenol removal rates were 71% and 75%, respectively, with methanol concentration of 500 mg COD/L for a total organic loading rate of 3.5 kg COD/(m3 x day) and a phenol loading rate of 0.6 kg/(m3 x day). The phenol removal rate was not improved with a higher methanol concentration of 1000 mg COD/L. Substrate utilization rate (SUR) tests indicated that the SURs of phenol were 106, 132, and 83 mg phenol/(g VSS x day) at methanol concentrations of 250, 500, and 1000 mg COD/L, respectively, and only 45 mg phenol/(g VSS x day) in the control reactor. The presence of methanol could reduce the toxicity of coal gasification wastewater and increase the biodegradation of phenolic compounds.
[Show abstract][Hide abstract] ABSTRACT: A two-continuous mesophilic (37 ± 2°C) UASB system with step-feed was investigated as an attractive optimization strategy for enhancing COD and total phenols removal of the system and improving aerobic biodegradability of real coal gasification wastewater. Through the step-feed period, the maximum removal efficiencies of COD and total phenols reached 55-60% and 58-63% respectively in the system, at an influent flow distribution ratio of 0.2 and influent COD concentration of 2500 mg/L; the corresponding efficiencies were at low levels of 45-50% and 43-50% respectively at total HRT of 48 h during the single-feed period. The maximum specific methanogenic activity and substrate utilization rate were 592 ± 16 mg COD-CH(4)/(g VSS d) and 89 ± 12 mg phenol/(g VSS d) during the step-feed operation. After the anaerobic digestion with step-feed, the aerobic effluent COD concentration decreased from 270 ± 9 to 215 ± 10 mg/L. The results suggested that step-feed enhanced the degradation of refractory organics in the second reactor.