Huiqiang Li

Removal of phenols, thiocyanate and ammonium from coal gasification wastewater using moving bed biofilm reactor

A laboratory-scale moving bed biofilm reactor (MBBR) with a volume of 4 L was used to study the biodegradation of coal gasification wastewater. Maximum removal efficiencies of 81%, 89%, 94% and 93% were obtained for COD, phenols, SCN(-) and NH(4)(+)-N, respectively. NO(2)(-)-N accumulation induced increase of effluent COD concentration when the hydraulic residence time (HRT) decreased. Phenols removal was not affected when the HRT decreased from 48 to 32 h. Effluent SCN(-) and NH(4)(+)-N concentration increased with the decrease of the HRT, and decreased gradually when the HRT returned to 48 h. Batch experiments were carried out to study performance of the suspended and attached growth biomass in the MBBR.

Treatment of coal gasification wastewater by a two-continuous UASB system with step-feed for COD and phenols removal

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.

Enhanced anaerobic biodegradability of real coal gasification wastewater with methanol addition

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.

Thermophilic anaerobic digestion of Lurgi coal gasification wastewater in a UASB reactor

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.

Inhibition and recovery of nitrification in treating real coal gasification wastewater with moving bed biofilm reactor

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.

Effect of nitrate concentration on performance of pre-denitrification moving bed biofilm reactor system in treating coal gasification wastewater

Abstract An anoxic moving bed biofilm reactor (ANMBBR) followed by an aerobic moving bed biofilm reactor (AEMBBR) operated as pre-denitrification system was used to investigate the effect of different influent NO3 −-N concentrations on performance of the pre-denitrification system in treating real coal gasification wastewater. Influent NO3 −-N concentration was controlled at 50, 100, 200, and 400 mg/L during the experiments. Evolution of COD and phenols in the effluent of the ANMBBR and AEMBBR, and performance of nitrification in the AEMBBR with different influent NO3 −-N concentrations were studied. Almost complete denitrification was achieved when influent NO3 −-N concentration was 100 mg/L. NO3 −-N and NO2 −-N accumulated in the effluent of the ANMBBR with influent NO3 −-N concentrations of 200 and 400 mg/L. NO3 −-N concentration of 400 mg/L facilitated high NH4 +-N removal efficiency in the AEMBBR when influent NH4 +-N concentration was around 165 mg/L. The ratio of CODconsumed/NO3 −-Nconsumed along w...

Scheme Design and Analysis on Biogas Liquefaction System

The biogas has important practical significance in solving the energy crisis as a kind of clean, renewable biological energy of ground. As the large-scale concentratedness of the biogas is produced, the liquefaction of the biogas is extremely urgent in technical research in China. According to the characteristic of the biogas, on the basis of mature natural gas purification and liquefaction technology, this paper discussed the small-scale biogas liquefaction system of the double purposes to purification, liquefaction and recovery of liquefied CO2. This paper provides the liquefaction biogas plant process chart, and system analysis, and the effects on the key parameters. Furthermore, the thermal parameters of the liquefaction cycle are presented. Finally, the economic investment of 5000Nm3•d small-scale biogas liquefaction cycle is emphatically analyzed, and the conclusion is that the payback period of the investment on the biogas liquefaction equipments is only 2.63 years. The result provides guidelines for the project feasibility analysis and design of the small-scale biogas liquefaction device.

Effect of recycle ratio on performance of pre-denitrification moving bed biofilm reactors in treating coal gasification wastewater

AbstractA lab-scale sequential anoxic moving bed biofilm reactor (ANMBBR) and aerobic moving bed biofilm reactor (AEMBBR) for pre-denitrification system were used to treat real coal gasification wastewater. Removal efficiencies of COD, phenols, thiocyanate (SCN−), ammonium (–N), and total nitrogen (TN) were investigated at different recycle ratios, and then NaHCO3 was added into the inlet of the AEMBBR to promote nitrification. Maximal removal efficiencies of COD, phenols, and SCN− were 84.2, 88, and 99.9% at a recycle ratio of 3.0, respectively. –N and TN removal efficiencies could achieve 97.4 and 78.2% with the addition of NaHCO3 (3 g NaHCO3 per day). Concentrations of –N and –N were always below 0.2 mg/L in the effluent of the ANMBBR. –N accumulation could be observed in the effluent of the AEMBBR after adding NaHCO3.

ECONOMIC ANALYSIS OF MIXED-REFRIGERANT CYCLE AND NITROGEN EXPANDER CYCLE IN SMALL SCALE NATURAL GAS LIQUEFIER

Two types of natural gas liquefaction processes, mixed-refrigerant cycle and nitrogen expander cycle were simulated. Their process parameters were optimized and compared. Their economic characteristics were analyzed. Although the mixed-refrigerant liquefaction process is more complicated than nitrogen expander cycle, its energy consumption is only 46% of the nitrogen expander cycle. The operation costs of mixed-refrigerant process are lower than those of nitrogen expander cycle, so the process is more competitive. The energy consumption of the optimized mixed-refrigerant cycle reaches the level of propane pre-cooled mixed-refrigerant process, which is usually used in base-load natural gas liquefaction systems and is the lowest of the mixed-refrigerant process. The process is comparatively simple, consumes less energy and has economic benefits, so the mixed-refrigerant process is the preferred choice for small-scale natural gas liquefaction device.

DESIGN AND ANALYSIS OF A SMALL-SCALE BIOGAS LIQUEFACTION CYCLE

The biogas has practical significance in helping to solve the energy crisis. This paper provides a small-scale biogas liquefaction scheme, the liquefaction flow diagram, and analysis of the impacts of key parameters. The thermal parameters of the liquefaction cycle are presented. The results provide guidelines for the design of small-scale biogas liquefaction systems.