Removal of phosphorus from anaerobic digested blackwater by precipitation with struvite from seawater and magnesium chloride

Abstract

Phosphorus is a finite resource with the largest remaining resources in West Sahara and China. India and Europe have no significant mineral Phosphorus. The increase of awareness about the recovery of Phosphorus as fertilizer is an important issue for the food security and environmental protection. In this thesis the recovery of Phosphorus was carried out by precipitating anaerobic digested blackwater with Magnesium Chloride (MgCl2.6H2O) and Seawater. The main purpose was to determine the effect of mixing ratio and pH on the removal of nutrients from blackwater. Based on the main goal two hypothesis were formulated, firstly addition of Mg source is an important factor on the removal efficiency of P. The use of ratio of struvite Mg :P 1.3:1 and 1:1 led to about 90% and 80 of P removal respectively. And Secondary hypothesis was that an increase of pH from 8.5 to pH 9 increase removal efficiency. To carry out the experiment digested blackwater was taken from Realtek laboratory and source of seawater was taken from Drøbak. The adjustment of pH was done by adding few drops of Sodium hydroxide. Analysis of nutrients was done by using LCK 350 and LCK303 methods and the reading was taken from using Hach Lange 3900DR. The results showed the highest total P removal of 99.7% with MgCl2 at pH 9 and Mg:P of 1.3:1 with MgCl2 and 96.3% with seawater. Also, removal of PO4-P removal efficiency was 99% at seawater with mixing ratio of 1:1 at pH 9 and the lowest value was 95.1% with MgCl2 at pH 8.5 mixing ratio 1:1.