Phosphorus recovery as a struvite from sewage sludge applying Box-Behnken experimental design method

Phosphorus (P) is one of the fundamental element for all living organisms. Phosphorus recovery technologies are developing day by day because of the realizing the importance of phosphorus. While recovering the phosphorus, pipeline's clogging problem which is one of the most important problem in wastewater treatment facilities is minimized and sludge storage problem decrease. In this study, phosphorus recovery potential of sludge filtrate which obtained by electro dewatering process was investigated. In this process, recycled sludge of secondary settling tank of Bolu Municipal Wastewater Treatment Plant was used. Phosphorus were recovered as a struvite which consists of magnesium, ammonium and phosphorus. Parameters, affecting the phosphorus recovery such as temperature, mixing time and concentration of the added magnesiumhydroxide are searched for determining the optimum conditions for the phosphorus recovery. Pumice stone was used for struvite crystals. Experimental results were evaluated by using the Box Behnken Design and Minitab 17 statistical software method. At the continuation of the experiments, determined three independent variables and three values for each independent were applied to the filtrate samples of sewage sludge . Determined ranges are 24-80 0C for temperature, 30-60 minutes for mixing time and 0.1-2.0 M for magnesiumhydroxide concentration. According to the comparison results between predicted and observed phosphorus recovery values R squared was found 0.91. The maximum phosphorus recovery condition was found at 800C sample temperature, 2.0 M magnesiumhydroxide concentration and 45 minutes mixing time and the maximum value for phosphorus recovery was found as 15.8125 mg PO4-P /L. According to our experimental and statistical studies' results phosphorus recovery percent is reached 37 percent as a maximum value. Temperature of the sample and magnesiumhydroxide concentration are the most important factors which affect the phosphorus recovery. Keywords: Phosphorus recovery from sewage sludge, struvite, wastewater treatment plant problems, MAP