ELOVAC®-P is a compact, skid-mounted vacuum degassing technology for digested sludge with simultaneous phosphate precipitation, which improves dewatering and reduces the phosphate return load. This technology is particularly beneficial for any anaerobic digestion plant with struvite scaling issues looking to improve dewatering and reduce polymer consumption.
Dissolved phosphate increases the water binding capacity of the EPSs and proteins (Kopp 2013). Therefore, there is an inverse relationship between the quantity of dissolved phosphate in the digested sludge and the solids in dewatering. The higher the concentration of phosphate, the lower the percentage of solids. Thus, precipitating >90% of the phosphate results in an improvement in dewatering and a reduction in polymer consumption.
Struvite buildup in pipes, valves and pumps compromises the operational efficiency of the treatment plant. Precipitating the phosphate with magnesium chloride in the digested sludge under controlled conditions minimizes the concentration levels of soluble phosphate, which prevents uncontrolled struvite scaling downstream the digester.
Although the centrate from the dewatering equipment only contributes 1-3% of the flow going to the headworks of the plant, the phosphate return load in particular can be as high as 10-30% in relation to the influent P-load to the WWTP. Therefore, especially at Bio-P plants, the phosphate load coming from the centrate adds a significant burden to the water treatment line. Especially in sludge treatment centers, the high phosphate and nitrogen return loads in wastewater treatment plants and related high ferric-dosing can affect the buffer capacity and therefore the efficiency of the nitrification step.