The Surplus Sludge Is Used As An Effective Electron Donor For Denitrification Carbon Source

At present,the traditional biological nitrogen removal technology is mainly used in the municipal wastewater treatment plants in China,but the shortage of denitrification carbon source has become an important factor restricting the efficiency of biological nitrogen removal.With the national attention to the concentration of ammonia nitrogen and total nitrogen in wastewater,the removal of nitrogen has become a necessary goal.At present,the carbon source is mainly the easily degradable organic matter,and its cost is very high.Therefore,finding low-cost electron donors to drive denitrification is an important target for many municipal wastewater treatment plants.At the same time,the plants will produce a large number of excess sludge every year,which needs to be treated and disposed.Excess sludge(biomass)potentially is a low-cost electron donor generated internally to the municipal wastewater treatment plants,but it has to be made more bioavailable.In this paper,based on the purpose of using excess sludge as the external carbon source of denitrification,the sludge acclimated under aerobic and anoxic conditions was treated by ultrasound and ultraviolet light,respectively.Taking sodium acetate as the reference,the difference of bioavailability between the two kinds of sludge was calculated by kinetics and stoichiometry,and the specific components of bioavailability in sludge were explored.In the course of the experiment,modern molecular biology technology,high-throughput sequencing,was used to explore the diversity of microbial communities.The main conclusions of this paper are as follows:(1)The supernatant of aerobic sludge and anoxic sludge after ultrasound treatment can be used as bioavailable electron donors for denitrification,mainly because ultrasound treatment destroys bacterial micelles in sludge and releases organic matter in flocs.The content of COD(PCOD)in the supernatant was increased.(2)After ultrasound treatment,the bioavailability COD of aerobic and anoxic sludge supernatant was 55% and 82% of the total COD(TCOD),respectively.After UV treatment,the bioavailability was increased by 19% and 4%,respectively.Compared with UV treatment,ultrasound treatment plays a more important role in improving the bioavailability of the two kinds of sludge.(3)After ultrasound treatment,the bioavailability of anoxic sludge supernatant was higher than that of aerobic sludge,the denitrification rate was 54% faster than that of aerobic sludge,and the denitrification rate was 48% faster than that of aerobic sludge after UV treatment.(4)The denitrification rate is related to the concentration of electron donors.In a certain range,the higher the concentration of electron donors,the faster the denitrification rate.(5)According to the relationship between the COD concentration C of sodium acetate and the denitrification rate k,the effective electron donor contents of the supernatant of aerobic and anoxic sludge after ultrasound treatment can be calculated to be 56% and 76% of the total COD(TCOD),respectively.(6)The particulate COD(PCOD)is the main component of bioavailable COD in aerobic sludge and anoxic sludge.The proportion of particulate COD in aerobic sludge and anoxic sludge is 82% and 91% respectively.(7)Although the microbial community in the reactor was not as diverse as the two kinds of sludge domesticated in conical bottle,there were more strains with denitrification function.