Advanced Nitrogen Removal Via Nitrite From Landfill Leachate By The Anaerobic-Aerobic Combined Process

Sanitary landfill method is commonly used to treat municipal refuse in China. Compared to other means, sanitary landfill is the cheapest. However, landfill leachate, a strongly polluted wastewater, has become the subject of recent interest. Leachate is considered the aqueous effluent generated as a consequence of rainwater percolation through wastes, the inherent water content of wastes themselves and biochemical processes in cells of waste. The pollutant composition of landfill leachate is very complicated, and its characteristics vary a lot depending on the environmental conditions. The concentrations of organic material and ammonia nitrogen are high in fresh leachate, while matured leachate contains relatively lower concentration of organic matter but higher concentration of ammonia nitrogen. High concentration ammonia nitrogen is considered as the main reason for low effciency in biological treatment of landfill leachate. Due to operation costs and other reasons, biological technologies are major methods to treat landfill leachate. The anaerobic-aerobic combined process is considered the most economy and effective method to degrade ammonia for landfill leachate treatment.Based on the above background, first of all, a system of a two-stage UASB and an anoxic/aerobic (A/O) reactor was fully depended on as biological treatment of the municipal landfill leachate without any pre-physicochemical process. Complete ammonium nitrogen removal via nitrite was achieved. The system decreased operational costs and energy consumption, and simplifed the conventional treatment processes as well. The process procedures as follows: Part of the recycled effluent as well as the inffluent of the system was pumped into the first stage UASB (UASB1). The organic compounds of landfill leachate served as the carbon source for denitritation of the recycled effluent in UASB1. Part of the raw organics was firstly depleted as carbon source for denitritation in UASB1, while simultaneous methanogenesis occurred. Most of the organic compounds of the UASB1 effluent were depleted via methanogenesis in UASB2. Recycled sludge from the clarifying tank was pumped into the anoxic zone, the first chamber of the A/O reactor, in which denitrification of NOX--N (nitrite and nitrate nitrogen) of recycled sludge was taken place. Nitrification of ammonia was carried out in the aerobic zone of A/O reactor.The fresh leachate was firstly treated by the system of a two-stage UASB and an anoxic/aerobic (A/O) reactor. The ratio of C/N of fresh leachate is very high. It had a good result of the treatment by using the the system of a two-stage UASB -A/O reactor. Partial nitrification with 88% of nitrite accumulation efficiency took place in the A/O reactor, and the ammonia removal efficiency was nearly 100% in the system.The system of a two-stage UASB -A/O reactor was used to treat mature landfill leachate. First of all, when carbon source did not add up to the system, the COD is used as carbon source of denitrification by the first UASB. It is short of carbon source of denitrification in the A/O reactor. Then, when some carbon source were added up to the first shelve of A/O system to advance the denitrification. Because the denitrification can produce some alkalinity, which it can complement some alkalinity by nitrification consumed, and it maintained pH at a suitable scope. By this way, the stable partial nitrification was successfully achieved. Partial nitrification with 87% of nitrite accumulation efficiency took place in the system. But when some carbon source did not add up to the system, the nitrite accumulation of rate was only 20%. The ammonia concentration of effluent leachate was 10 mg/L. The ammonia removal efficience was 99.6%. But when some carbon source did not add up to the system, the ammonia removal efficience was 92% in the system.But the removal of total nitrogen (TN) could not reach below 40 mg/L which was requested by the release of new national standard for pollution by only using a two-stage UASB -A/O reactor. In order to reduce the TN concentration further, the process was improved. The final effluent of A/O reactor was further treated by SBR. The system of a two-stage UASB-A/O-SBR was utilized to treat both fresh and mature landfill leachate to remove nitrogen thoroughly.The results of the experiment showed as follows: The ammonia nitrogen concentration in the effuent of the system was no more than 15 mg/L. The nitrite nitrogen and nitrate nitrogen concentrations in the effluent were no more than 4 mg/L. The TN concentration was nearly 30 mg/L. The ammonia and TN removal efficiency was nearly 100% in the system Therefore, the two-stage UASB-A/O-SBR system was a highly effcient process to treat both fresh and mature landfill leachate.The experiment investigated the style of carbon source added when mature landfill leachate was treated. The influent leachate is mixed by raw leachate as well as domestic wastewater in a ratio of 1. The external carbon source (sodium acetate anhydrous) is added in order to enhance the C/N ratio from 1.7 to 3.0. The system of a two-stage UASB-A/O-SBR was utilized to treat mature leachate to remove nitrogen thoroughly. Through the cooperative inhibition of the free ammonia (FA) and free nitrite acid (FNA), the particial nitrification is achieved stably in the A/O reactor with more than 70% of the nitrite accumulation ratio. The nitrite and nitrate which are produced by the nitrification could be removed completely in SBR. The ammonia concentration of final effluent is less than 2 mg/L, and its removal efficiency is 99%. The total nitrogen mass concentration of final effluent is about 26 mg/L, and its removal efficiency is about 98%.A system consisted of two - stage UASB- A/O reactor was used to study the partial nitrification of the municipal landfill leachate with high ammonia concentration. The study which used real landfill leachate showed that if the concentration of FA was more than 40 mg/L, a stable partical nitrification could be successfully achieved. But if the FA concentration was more than 160 mg/L, the nitrification could be inhibited. And raw leachate was diluted in order to degrade the concentration of FA. Then the partical nitrification was restored. Partical nitrification with 92.17% of nitrite accumulation efficiency took place in the system, and the ammonia removal efficiency was 98.6% in the system. In a word, the concentration of FA was an important factor to achieve a short-cut nitrification of the municipal landfill leachate.In order to investigate the effects of free ammonia (FA), temperature and free nitrite acid (FNA) on partial nitrification, a system consisting of a two - stage UASB and an A/O reactor was used to treat leachate from municipal landfill. The results for three phases showed that a suitable FA concentration range exhibited negligible effect on partial nitrification. In this experiment when FA concentration was between 1 mg/L and 30 mg/L , stable partial nitrification could be achieved and maintained successfully. However, when FA concentration was over 250 mg/L, the entire nitrification process could be inhibited. Temperature was not the key factor to partial nitrification. In the third phase, although the temperature was very low (16℃～18℃), partial nitrification occurred and was successfully maintained with a nitrite accumulation rate of 88% in the A/O reactor. When pH was more than 8.5, the influence of FNA on partial nitrification was minimal. In conclusion, FA concentration was a major factor to achieve a partial nitrification of municipal landfill leachate.Particial nitrification - anaerobic ammonium oxidation process were used to treat mature leachate in order to remove nitrogen thoroughly. The system of a two-stage UASB-A/O-SBR was utilized to treat mature landfill leachate this stage. In the A/O reactor, FA concentration inhibited only NOB but not AOB. Thus, stable partial nitrification was obtained. Part of the recycled effluent of A/O reactor as well as the inffluent of the system was pumped into UASB1. The nitrite of the recycled effluent and part of the inffluent ammonia nitrogen were removed by Anammox. Because part of the ammonia nitrogen was removed, the inhibition of the high concentration of ammonia nitrogen was avoided. The results of the experiment showed as follows: The ammonia nitrogen concentration in the effuent of the system was only 15 mg/L. Nitrite accumulation efficiency was 87.5%.The effluent of A/O reactor was further treated by SBR. The external carbon source was added into SBR. Denitrification was ceased after the 4th hour. After denitrification, the nitrite nitrogen and nitrate nitrogen concentrations of final effluent were less than 1 mg/L. The TN concentration of final effluent was only 29 mg/L and the ammonia nitrogen concentration of final effluent was 7 mg/L.Therefore, the ammonia nitrogen and TN removal efficiency could reach nearly about 100% by the Anammox of anaerobic, the particial nitrification of A/O reactor and the denitrification of SBR. This combined process is the most economy and high effciency method in biological treatment of landfill leachate.