Biological Treatment Of Raw Coking Wastewater By Aged-Refuse-Based Bioreactor

Coking wastewater is a highly contaminated industrial organic wasteswater with potential toxicity and its treatment is usually quite difficult as it contains high strength persistent organic pollutants. In our previous research work, it has been found that the aged-refuse-based bioreactor can be used for the effective treatment of refuse leachate, feedlots wastewaters, dying wastewaters, ect. Hence, in this work, this innovative bioreactor was also used for the treatment of raw coking wastewater. The optimum operational parameters were explored and the flowsheet for pilot test were proposed, using the wastewater from Nanchuan Daxing Coalchemical Plant.Two flowsheets was investigated on the feasibility of treatment of the wastewater by ARBBRs. The COD of effluent of AO (Anoxic /Oxygenated) system fluctuated from 138 mg/L to 158mg/L and ammonia nitrogen concentration was about 800mg/L. The removal ratio of COD and ammonia nitrogen was 94%, 98% respectively. When the wastewater was treated by OAO (Oxygenated/Anoxic /Oxygenated) system, the COD of the effluent ranged from 97.3~138mg/L and the removal ratio was about 95%. The treatment cost was estimated to be around 5.25 yuan/ton. There was little sludge generated in the process and the process was very stable, easy to operate and manage.When the effluent of O2 unit was mixed with the origin coking wastewater with a recirculation ratio of over 1, floccule was generated in the mixture and can be separated from the mixture, leading to a removal of COD subjected to pH of the mixture. The Anoxic unit could bear dramatic change of COD and pH of influent, and a further reduction of COD can be obtained by the addition of origin wastewater. When the origin wastewater was treated with a recirculation ratio of 1 by the 2-metre long O unit, the COD and ammonia nitrogen concentration in the effluents can be reduced to about 200mg/L and 700mg/L, respectively, and can be reduced further as its loading was decreased or the height of bioreactor was increased.It is considered that around 78% of COD was removed in A unit by denitrification. The ammonia nitrogen removal in O unit should be better than A unit and simultaneous nitrification and denitrification in O unit may occur. The average total nitrogen removal in O unit was 99.4g/m~3/d.