Study On Recovery And Reuse Of Aluminum And Iron Coagulants From Water And Wastewater Treatment Sludges

In China, large quantities of chemical sludge are produced in water treatment process every year which has a bad environmental impact without proper disposal. Nowadays, the most common disposal method of water treatment sludge is some type of dewatering and land disposal which will occupy vast land and pollute the surroundings. Water and wastewater treatment sludge disposal in future certainly will stress sludge utilization and reduction.Acidification of sludge can dissolve aluminum or iron, and reduce the volume and dry weight of the disposal sludge. The recoverd aluminum or iron coagulants also contain other substances that are soluble under highly acidic conditions or that exist as colloids. Generally speaking, the purity of the recovered coagulants may be not sufficient to justify its reuse in water treatment. Chemically Enhanced Primary Treatment (CEPT) is a wastewater treatment process that has higher efficiency, lower energy consumption, less running cost, and convenient management and maintenance. At present, China is a developing country that the water enviroment has been badly polluted and the capability of wastewater treatment is lower. Thus, the recovered coagulants can be used in CEPT process in wastewater treatment.In this paper, the recovery and reuse of the coagulants from water and wastewater treatment sludges were investigated. An acidic recovery process was adopted to recover the coagulants, and the recovered coagulants were reused in wastewater treatment process.The optimal recovery conditions of aluminum and iron coagulants were studied, and the linear relationship between the total solids reduction and the coagulants recovery rate was put forward. System pH value, mixing time and the quality of sludge are three main factors that have effect on the recovery rates of coagulants. The recovery rates were greatly affected by pH value.In this study, the components of the recovered coagulants were analyzed. The results showed that the heavy metals and organic materials contents of the recovered coagulants were higher than the commercial coagulants for the same coagulant concentration. The metals and organic materials could build up if continual recycling was practiced. And it may be affect the quality of effluent.The experimental results of the reuse of recovered coagulants in CEPT process showed that the removal efficiency had no obvious difference between the recovered coagulants and the commercial coagulants.Acidification of sludge to recover and reuse the coagulants can achieve utilization and reduction of the water and wastewater sludge. This sludge disposal method can both gain economic and environmental benefits.