The Treatment Of Dairy Farm Wastewater By Biological Aerated Filter And Its Combined Processes

Currently the treatment technology of dairy farm wastewater under the dry dung cleaningup process is still not mature enough. China has further raised the discharge standards the in thenewest ‘Discharge standard of water pollutants for livestock and poultry breeding’（suggestion-soliciting draft）, so it is necessary to enhance the treatment effect and develop newtreatment processes.The integrated biological aerated filter （BAF） with aeration section andnon-aeration section and its combined processes were adopted to investigate the performancesand process conditions on the treatment of dairy farm wastewater to meet the requirement of thedischarge standards.BAF and sequencing batch reactor （SBR） were adopted to investigate the influences ofdifferent operating conditions on the pretreatment to dairy farm wastewater. The combinedsystem of BAF with bottom aeration mode and BAF with mid aeration mode, and the combinedsystem of SBR with suspended packed materials and BAF with mid aeration mode wereestablished. The best treatment efficiency and the optimum conditions were determined throughthe regulation of different working conditions, and the results are compared with the integratedBAF. The following contents were investigated:1. Economical operating modes and processconditions treated by integrated BAF which could meet the requirement of discharge standard.2.The optimal process conditions of pretreatment by bottom aeration mode BAF.3. Theinfluences of operation cycle, aeration and aeration mode （continuous aeration and intermittentaeration） on the treatment effect of pretreatment by SBR reactor.4. Performance of twocombined processes under different operating conditions, and the optimization of operatingconditions.The main results were obtained as follows:（1） The effluent ammonium-nitrogen （NH₄⁺-N）, total nitrogen （TN） and chemical oxygendemand （COD） could meet the limit-value requirements of the newest ‘Discharge standard ofwater pollutants for livestock and poultry breeding’（suggestion-soliciting draft） in thedirect-discharge mode for the newly-established breeding farm while the integrated BAF wasadopted to treat dairy wastewater under dry dung cleaning up process. Under the condition ofhydraulic retention time（HRT）12h, the recirculation ratio2:1and the air/water ratio20:1whenthe volumetric ratio of aeration section to non-aeration section was2:1, the averages of effluentNH₄⁺-N, TN and COD were2.76mg/L,20.42mg/L and82.0mg/L, respectively, when theaverages of influent NH₄⁺-N, TN and COD were94.20mg/L,94.99mg/L and459.5mg/L,respectively.（2） The BAF with bottom aeration mode has better removal efficiency for NH₄⁺-N, CODand suspended solid （SS） than TN and TP. Under the condition of HRT4h and the air/waterradios10:1and5:1, the removal rate of NH₄⁺-N could achieve a rate of80%, and the average removal rates of the two different air/water ratio were82.87%and79.25%, respectively. Theaverage COD removal efficiency in a stable runtime is as high as95%, and the effluent CODwas relatively stable at an average of36.1mg/L. SS reduced to an average concentration of7.29mg/L from the average concentration of236.91mg/L, the average removal rate was96.92%.（3） The removal of NH₄⁺-N, TP, TN, COD, SS through the SBR with suspended packedmaterials was evidently efficient. When the operation cycle period was4h, the hydraulicloading rate was0.4L/L and the aeration intensity was1.6L/（L·h）, the removal rate of NH₄⁺-Ncould be up to62.91%, the effluent average NH₄⁺-N concentration could be41.10mg/L; Whenthe cycle is6h, the highest removal rate of TN could reach70%, and the effect of intermittentaeration mode was better than continuous aeration one; the average removal rate of COD was91.0%; the effluent average concentration of TP was1.75mg/L, the average removal rate was33.64%; the average removal rate of SS could reach97.99%.（4） The combined system of SBR with suspended packed materials and BAF with midaeration mode has a better treatment efficiency of NH₄⁺-N, TN, TP and SS than before. Theeffluent concentration of NH₄⁺-N was below5mg/L, and the average removal rate was up to94.4%; with the operational conditions of operation cycle period4h, each cycle with hydraulicloading rate0.4L/L and aeration intensity0.8L/（L·h） under the intermittent aeration mode, andintegrated BAF running conditions were the air/water radio4:1, HRT4h and recirculation ratio2:1. The combination system was best on the removal of total nitrogen, and the maximumremoval rate might be up to71.35%. The system had an obvious effect on TP removal, and theaverage removal rate was43.23%.This research indicated that the integrated BAF and the combined process system ofSBR with suspended packed materials and BAF with mid aeration mode could treat the dairyfarm wastewater efficiently under the dry dung cleaning up process, and the effluent qualitycould meet the limit-value requirements of the emission standards. The HRT and air demand ofthe combined process system of SBR with suspended packed materials and BAF with midaeration mode were less than that of the integrated BAF, and the costs of infrastructure andoperational management were less accordingly. The combined process of SBR with suspendedpacked materials and BAF with mid aeration mode therefore have a broader prospect inengineering application.