Research On The Treatment Of Coal Gasification Wastewater By Anaerobic-aerobic Batch Process

The rapid development of coal gasification industry in our country isdecided by the energy characteristics of “rich in coal, short of oil and gas”.But meanwhile the effective treatment of the wastewater has become thebottleneck that restricts the development of the coal gasification industry.The coal gasification wastewater is consisted mainly by large quantities ofgas washing wastewater which contains high concentrations of toxicchemicals such as phenolic compounds, aromatic hydrocarbons,heterocyclic compounds, ammonia, cyanide and is hazardous to bothhumans and environment. The combination of biochemical treatment andadvanced treatment is the trend of coal gasification wastewater treatment,but in long-term’s of practice, the biochemical treatment often has defectssuch as unsatisfied efficiency, large quantities of sludge, lack of stability,long treatment process, large area, high cost, et al. And as artificialwastewater is often used to study the treatment efficiency and mechanismin lab scale study, the results can’t represent the treatment efficiency of realwastewater. This research applied hydrolytic acidification-aerobic processto treat coal gasification wastewater, took advantages of differentbiodegradabilities of acidification bacteria and aerobic bacteria andimproved the overall treatment effect. During the research, real coalgasification wastewater which was recycled of phenols and ammonia wasuesed to study the removal efficiency of pollutants in different reactors andthe effects of acidification as pretreatment. Meanwhile, degradationkinetics of pollutants were modeled, diagrams of carbon balance during hydrolytic acidification process were drawn, and GC-MS was applied tofurther analyse degradation rules of anaerobic and aerobic process.The influnt COD, total phenols, volatile phenol and ammonianitrogen were950-1200mg/L,190-240mg/L,83-115mg/L and80.8-110.4mg/L, after48h acidification-48h aerobic treatment, the removal ratioscould be59.6±0.6%,84.6±1.4%,99.8±0.2%and98.7±1.2%respectively.The anaerobic reactor played a major role in the removal of COD and totalphenols, and removed69.5±1.9%of the COD and98.6±1.4of the volatilephenol, so the volatile phenol was almost degraded in the anaerobic reactor;After24h acidification-48h aerobic treatment, removal ratios of COD,total phenols, volatile phenol and ammonia nitrogen could be65.1±1.0%,79.6±2.0%,99.5±0.5%and99.0±0.9%respectively. As the acidificationtime was shortend, removal ratios of COD, total phenols and volatilephenol in aerobic reactor increased, and most total phenols were degradedin the aerobic reactor. The removal efficiency of the system was greatlyincreased by constantly acclimatizing the sludge, therefore, shortened thereaction time and reduced the operating cost.The system showed superiority in the treatment of ammonia nitrogenwith the effluent concentration less than0.5mg/L, which was much lowerthan that in the existing biochemical treatment examples of coalgasification wastewater. This was mainly because of the effects of thehydrolysis acidification pretreatment, which reduced the burden on theaerobic reactor and weakened the poison and inhibition on nitrifyingbacteria. Volatile phenol in the wastewater accounted for about37.7%-56.9%of total phenols, and its removal ratio could reach100%,significantly higher than that of total phenols. Volatile phenol was the mainpart of the reduced phenolic compounds. Under the experimentalconditions, the degradation of COD, total phenols, volatile phenol andammonia nitrogen in the anaerobic and aerobic systems both accorded withthe characteristic model of first-order reaction kinetics.The carbon balance test showed that after48h hydrolytic acidification process, methane concentration was high in the gas phase while ICconcentration was low in the liquid phase, so the reaction system hadentered the methanogenic stage; After24h hydrolytic acidification process,hydrolysis acidification stage became the dominant stage, and organicswere mainly removed by hydrolysis acidification process.Results of GC-MS analysis showed that the main influent pollutantswere phenolic compounds, followed by carboxylic acids, ketones, alkanesand heterocyclic compounds. Most phenols, carboxylic acids and ketoneswere degraded in the process of bio-treatment. However, some refractorycompounds with complex structures such as heterocyclic compounds,polycyclic compounds, lipids, alkanes and amines were remained in theeffluent. So although this system had high removal ratios of differentorganics, the effluent COD and total phenols were still about370mg/L and30mg/L, which were higher than the national emission standards and needsubsequent advanced treatment.