ELOVAC®-P

High phosphate contents in the digested sludge for example at Bio-P plants increases the water binding capacity of EPS and proteins. Precipitating the dissolved phosphate reduces the water binding capacity and therefore increases dewaterability of the digested sludge. Samples from digested sludge in the Lingen WWTP, Germany before and after ELOVAC®-P were examined. The TR(A)-parameter assessing the achievable dewatering result of sludge (method developed by Dr. Julia Kopp, wastewater treatment engineer ) showed a significant increase in the dewatering result of more than 5% points. Based on these results, disposal cost savings of approximately 20% can be attributed to the vacuum degassing with P-precipitation as a stand-alone technology.

Vacuum degassing slightly raises the pH of the digested sludge and with the addition of magnesium chloride; the controlled struvite precipitation takes places in the reactor tank without growth or separation of the struvite. The micro-crystals are the size of a fine sand, which means that they do not attach to pipes, tanks or dewatering equipment. Because the pH goes up only slightly (<8) and the concentration of phosphate is reduced considerably, the risk of struvite formation downstream is mitigated.

Compared to conventional technologies, the approach of ELOVAC®-P is different in the precipitation of the phosphate: achieving no growth of the precipitates and no separation of the crystals. Therefore, the benefits of this approach are unique: a very small tank reactor volume (approximately 50 times smaller than the standard technologies) because the retention time for the chemical reaction takes place in seconds rather than hours. Additionally with ELOVAC®-P we avoid wear of the dewatering
equipment due to abrasive struvite crystals.

ELOVAC®-P is a modular system that can handle any plant size. The different models of ELOVAC®-P range from 10 m³/h to 50 m³/h throughput of digested sludge. The system comes pre-assembled and it is skid mounted so there is minimal on-site construction required.

Conventional phosphate precipitation processes raise the pH of the digested sludge either by adding caustic soda, thus consuming chemicals, or by aeration, and therefore stripping CO₂. With aeration, not only is CO₂stripped, but also methane is released into the atmosphere. With ELOVAC®-P, the vacuum degassing not only causes an increase in the pH by withdrawing CO₂, but the vacuum captures the biogas that is not “diluted” with air, which prevents methane being emitted into the atmosphere. The additional biogas can be then utilised to operate the unit, making ELOVAC®-P an energy positive system.

The quality of biosolids produces at the plant as a fertiliser for agricultural and land cultivation improves with ELOVAC®-P because the miniscule struvite crystals remain in the dewatered cake.