Transformation Of Nitrogen Compounds In Coking Wastewater During Biological Treatment Process And Ozone Selective Oxidation Process Analysis

Coking wastewater is a typical industrial wastewater containing substantial amounts ofnitrogen but limited amounts of phosphorus. The choice of the nitrogen removal processshould consider not only the denitrification efficiency of the process itself, but also thevalidity of the nitrogen removal process to the target water. Establishing of total nitrogen(TN)composition evaluation system which is suitable for coking wastewater can help uscomprehend the TN composition of coking wastewater and provide guidance and basis forthe optimal design of coking wastewater nitrogen removal process.There are multiple inorganic and organic nitrogen compounds in the coking wastewater;the transformation and removal of them in an order of preference is an important factoraffecting the technologies selected for the wastewater treatment plant (WWTP). Therefore,identifying the nitrogen compounds in the raw wastewater and understanding how they canbe transformed are of crucial importance to optimize operational parameters for the WWTP.This study aims to (i) detect different forms of nitrogen compounds in the raw wastewaterand the effluent from the biological treatment,(ii) determine the concentrations of inorganicnitrogen compounds and some of organic nitrogen compounds available in differ units, and(iii) investigate the transformation and removal of some specific nitrogen compounds.Samples were taken from a practical coking WWTP that treats wastewater delivered from a330×104t/a coking-producing factory and adopts an O1(aerobic)/H (hydrolytic)/O2(aerobic)biological process as the core technology. Results showed that inorganic nitrogen compoundsin the coking wastewater were primarily composed of ammonia (33.6%), cyanide (7.5%), andthiocyanate (40.4%) with a total nitrogen concentration about240mg·L-1. Organic nitrogencompounds in the coking wastewater consisting of14kinds of amines,22kinds of organicnitriles and76kinds of nitrogen-containing heterocyclic compounds were detected, with atotal nitrogen concentration about50mg·L-1. After the first aerobic biological treatment,cyanide and thiocyanate were oxidized to ammonia, and the forms of some organic nitrogencompounds were also changed. After the hydrolytic process, nitrogen-containing heterocycliccompounds were transformed to ammonia and nitrate from the cycled O2effluent waseventually reduced to nitrogen. After the second aerobic biological treatment, ammonia was oxidized to nitrate. It was found that nitrate accounted for more than70%of total nitrogen inthe biological effluent. The experiment results indicated that the transformation of nitrogencompounds in the coking wastewater was complicated, depending on the properties ofreactors and their operational conditions. Our findings suggest that the control of totalnitrogen in the coking WWTP should take into consideration the identify of nitrogencompounds, the combination of different treatment processes, and the optimization ofoperational conditions.Thiocyanate is the TN core component of coking wastewater, and it can be oxidized byozone. The study investigated the reaction between thiocyanate and ozone in differentconcentrations of ozone, different initial pH and with metal ion added. Results showed thatfinal products are different when different initial pH. The experiment results indicated thatmetal ion can catch the thiocyanate, and solw down the reaction between thiocyanate andozone.