Chemical Cracking And Carbon Source Recovery Process Of Excess Sludge In Sewage Treatment Plant

The utilization rate of activated sludge process still takes up a large proportion in the sewage treatment plants in small towns and cities,medium-sized and large cities in China.Although the efficiency and stability of sewage treatment plant is obvious,the disposal of excess sludge following.Solid content as low as 0.5%¹% of the excess sludge,which containing a lot of poisonous things,such as pathogenic organism,hazardous,noxious physical and corruptible microorganisms or chemical substances.Simultaneously,the excess sludge has the characteristics of large bulk,expenditure of capital construction and runing is costly and higher secondary pollution.The purpose of this research is to provide the thought and direction of the waste sludge reduction in wastewater treatment plants,the recovery eand utilization of carbon supply and the removal of nitrogen and phosphorus resources in the plants.In order to realize the sludge reduction and the recycling of the carbon,the removal of nitrogen and phosphorus of the sludge can be used to maximize the utilization of the sludge organic carbon.Sludge cracking is a commonly used method by researchers at this stage.It is a simple and effective method for sludge pretreatment.It mainly consists of three major categoriess:physics,chemistry and biology methods.By comparing the advantages and disadvantages of the various principles of sludge cracking,combined with economic and laboratory conditions,chemical combination cracking is selected in this project,that is,alkali+oxidant combined cracking form.The research mainly includes three steps: optimizing oxidant,individual cracking,alkali and optimizing oxidant.The optimum parameters are determined b y controlling the reaction time,pH value,dosage of reagents and the indexes of sludge under different control conditions.The hydrolysis rate v?N?>v?C?in the crack solution can be achieved by controlling the optimized pH value,temperature and load.The hydrolysis rate v?N?> v?C?in the solution of the sludge pretreatment can be further determined by controlling the pH value,temperature and load.Under the premise of less organic carbon consumption,organic nitrogen in the crack solution may be converted into ammonia nitrogen,and the occurrence of denitrification and nitrification can be avoided.After pretreatment of sewage sludge solution,the concentration of ammonia nitrogen in water phase is higher.In the nitrogen and phosphorus ratio is too large,can use a high concentration of ammonia in the hydrolysis solution by adding magnesium salt to form struvite precipitation,removal of orthophosphate,then coupling aeration to remove ammonia.Therefore the use of stripping and struvite?MAP?coupling method for removing high concentration of ammonia and phosphate solution liquid,increase the use of crack liquid carbon source.The liquid sludge disintegration as raw water,to blow off method,single MAP method and two coupling of magnesium salts,air volume,pH,Mg/P value and reaction time on nitrogen and phosphorus recovery effect,compared with the three methods,considering the effects of recycling and economic factors,the optimum reaction parameters of each phase should be methods.The experimental results show that the sludge disintegration in continuous wave under the condition of adding alkali type II oxidant sludge had the best effect,namely: alkali +II oxidation agent,alkali +I oxidation agent,II oxidation agent,I oxidation agent.The best reaction parameters are: reaction time 2h,pH=11,II oxidant dosage is 20g/kgSS.The data,under this condition,the removal rate of SS was 28.7%,the removal rate of VSS was 38.45% SCOD;the relative concentration of sludge 209.5mg/L to 4945.23mg/L,increased by 22.6 times;the concentration of NH₄⁺-N from sludge 27.26mg/L to 175.26mg/L,increased by 5.42 times.The best parameters were as follows: reaction time 1h,reaction temperature 25?,crack solution and inoculation sludge ratio of 2:1.Under this condition,the concentration of SCOD decreased to 19.3% with the solution of 4320.45mg/L,and the concentration of NH₄⁺-N increased to 198.37mg/L,which was 20.2% higher than that of the solution.Besides,protein concentration changes little.The N,P in the aqueous phase after the fermentation of the sludge solution is mainly in the form of ammonia nitrogen and orthophosphate,and the calculated molar ratio of ammonia nitrogen and orthophosphate is 33.6:1,the value is larger.The optimum experimental parameters were as follows: adding magnesium salt?Mg/P = 1.3?and stirring?30??for 10 mins,controlling p H at 9,combined with stripping for 6 h.Under these conditions,the removal rates of NH₄⁺-N and PO₄^3-were 94.4% and 84.6%,respectively.