Study On Scale Inhibition Process Of Landfill Leachate By Anaerobic Treatment

Landfill leachate is a high-concentration organic wastewater commonly used in the sewage treatment industry.It must be treated to reduce the harmful substances in the leachate and reach the discharge standard before it can be discharged.When the leachate was treated by the upflow anaerobic sludge blanket reactor（UASB）,it was found that a large amount of scale was generated in the anaerobic treatment structure and its accessories.The main component of the scale was detected and analyzed as carbonic acid.calcium.The scale grows faster and needs to be cleaned up in time.At present,the commonly used descaling method is the physical cleaning method,but this method not only needs to repeat cleaning,but also requires a lot of manpower and material resources,the operation process needs to consume a certain time,and when the scale is cleaned,the landfill leachate treatment needs to be stopped.The process reduces work efficiency and increases operating costs.According to the problem of serious scaling of the anaerobic device of landfill leachate and its accessories,according to the UASB production equipment,a set of experimental devices were designed according to the scale,and the water quality indicators during the operation of the monitoring device were ensured to ensure that the experimental device maintains a good state.During the operation of the experimental device,the pH value of the original leachate entering the experimental device ranged from 5.14 to 6.71,the pH inside the anaerobic tank was 7.50 to 8.30,and the pH range was normal;the average COD of the leachate was 63758 mg/L.The anaerobic treatment of the anaerobic system of the device reduced the average COD to 7633mg/L,the average COD removal rate was around 88%,and the average VFA reduction rate was above 80%.The internal SS concentration was 11.48 g/L.and the highest value can reach 57.35g/L.The monitoring results show that the experimental device was in good operating condition.The equilibrium analysis of scaled calcium ions showed that the proportion of calcium deposits into the anaerobic tank was about 90%.Therefore,the leachate was pretreated by chemical precipitation method to remove the scaled calcium ions in some landfill leachate and reduce the entry.The amount of calcium in the anaerobic fluid.Sodium phosphate and sodium oxalate were used as reagents for pretreatment of landfill leachate by screening the pretreatment experiments.The experimental results show that increasing the pH was beneficial to the production of phosphate precipitates.When the pH of the reaction was controlled at 6.0⁷.0,the stirring rate was easier to use 300 r/min,the reaction time was controlled within 10 hours.Static and settling time was controlled between8 and 10 h.When the pH of the reaction system was controlled to be around 6,the molar ratio n_（Ca）:n_（P）=1:0.35¹:0.55 was economical,and the reagent was added with n_（Ca）:n_（P）=1:0.40.At the time,the calcium ion concentration was reduced from 2706 mg/L to 1255 mg/L,and the calcium ion removal rate was 53.6%.The main factors affecting the calcium removal of the sodium oxalate reagent are the dosage of the reagent,and the secondary factors are the pH value and the reaction time.When the pH of the reaction system was 6,the calcium content of the leachate was 3101 mg/L,and the sodium oxalate reagent was added in a ratio of n_{（calcium）:}n_{（sodium oxalate）}=1:0.50,the calcium ion removal rate was as high as 49.5%.The time was 3hours and the precipitation process can be completed in 5 minutes.Considering the cost,the descaling reagent used a sodium phosphate reagent.The results showed that the average calcium ion content in the second stage before dosing was 2740 mg/L.The average calcium ion content in the third stage decreased to 1541 mg/L after the addition,the reduction rate was43.8%,and the amount of calcium flowing into the experimental device was reduced.The average amount of deposits per week before dosing in the oxygen tank was 185.1μm/week,the average value per week after dosing was reduced to 88.5μm/week,the average scale thickness was reduced by 52.2%,and the water quality before and after dosing.The indicator was normal.