Treatment Of Phenolic Wastewater By Alum Sludge-based Constructed Wetland

Phenolic wastewater contains different kinds of pollutants such as refractory organics（phenols,MACHs）and inorganics（ammonia nitrogen,sulfides,cyanide）.The components of phenolic wastewater are very complex.Some of them have the potential of carcinogenicity,teratogenicity and mutagenicity.There should be proper treatment of phenolic wastewater before it is discharged,otherwise it will cause serious environmental pollution and endanger human health.To reduce the negative influence of phenolic wastewater on water quality and environment,most countries have set up the critical effluent standard,and the effluent of phenolic wastewater treated by traditional treatment process including dephenolization,ammonia evaporation and biochemical reaction cannot meet the standards in most cases.Therefore,it is critical to develop the advanced treatment of phenolic wastewater.In this study,the possibility of using alum sludge-based constructed wetland to treat phenolic wastewater was tested prior to the trials of phenol adsorption by the alum sludge.The main research contents and conclusions are as follows:1)Alum sludge was used as the adsorbent to immobilize phenol in the aqueous solution,while the effects of alum sludge particle size,dosage,initial phenol pH and concentration on the absorption process were studied through the static absorption experiments.The results showed that various factors can lead to the enhanced adsorption process for phenol removal,such as the large quantities and fine grains of alum sludge,acid pH and high initial phenol concentration of the aqueous solution.In addition,Langmuir isotherm can describe the adsorption characteristics,while the maximium adsorption capacity of phenol was 19.92mg/g.2)Response surface methodology（RSM）was used to optimize the adsorption behabiour under several factors.As the result,the RSM indicated that pH,the initial phenol concentration and contact time had strong influence on adsorption reaction.The maximum value of the phenol adsorption capacity would be 20.8577 mg/g under the condition of the RSM optimization（the alum dosage of 3 g/L,the pH value of 8,the initial phenol concentration of 120 mg/L,the contact time of 120h）,and the reliability of the former model was 0.957.3)An alum sludge-based constructed wetland was developed to treat phenolic wastewater deeply.The effects of different operation conditions（phenol concentration and aeration）of the constructed wetland on COD,NH₄⁺-N,total phosphorus and phenol were studied for 220days’operation of the system.The alum sludge-based constructed wetland system has demonstrated excellent treatment performance,with average removal rates of 75.82±16.39%,97.97±1.81%,89.37±10.48%for COD,total phosphorus and phenol,respectively.For NH₄⁺-N removal,this system showed a relatively low efficiency,with the average removal rate of 30.03±27.48%.Moreover,aeration had a greater impact on the removal of NH₄⁺-N.After applying aeration,the average NH₄⁺-N removal rate was enhanced to 44.71±17.41%from 26.72±11.34%.4)The micro appearance characteristic and microbial population of the alum sludge substrate before and after adsorption were analyzed to explore the mechanism of pollutant removal in this system.The results showed that the alum sludge had a higher specific surface area which was helpful for adsorption,while several functional groups adhering to the alum sludge surface can react with phenol in aqueous solution.Moreover,the types and amounts of microbes found in different parts of the wetlands system were also different.Although there were some phenol-degraded bacteria,the amount of them was small and hence played a relatively small role on phenol removal.Therefore,it is understand that in the alum sludge-based constructed wetland system,phenol removal was mainly relied on the adsorption of the alum sludge.