| Description |
Activated sludge process (ASP) is the most common method for wastewater treatment of domestic wastewater. In ASP, a consortium of microbes is used to consume different contaminants of concern using redox chemistry in which case, microbes gain energy through substrate partitioning. The main contaminants of concern are carbon, nitrogen (N) and phosphorus (P) in municipal wastewater with the latter two collectively known as nutrients. ASP is a robust process with proven performance metrics. Between nitrogen and phosphorus, phosphorus is the main nutrient of concern because it is often cited as a limiting nutrient for biota. Furthermore, as a useful fertilizer, phosphorus is essential for plants and as a result, there is a global demand for P. Unfortunately, P is limited in nature with only five countries in the world supplying the total P demands. Hence, the focus of wastewater treatment management is changing from the removal of P to the recovery of P. A study was conducted at Central Valley Water Reclamation Facility (CVWRF) to evaluate the P recovery potential at different segments of the treatment train. A P mass balance was also conducted under a hypothetical scenario, where enhanced biological P removal was assumed at CVWRF. Results show that while aluminum was the superior chemical at removing phosphorus, all chemicals were successful at a rate of over 80% P removal at the optimum pH value. Magnesium, on the other hand, was superior at nitrogen removal. The sludge and filtrate have higher dissolved P loads, making them ideal areas for phosphorus removal and recovery. The installation of a Biological Nutrient Recovery (BNR) system with Enhanced Biological Phosphorus Removal (EBPR) would also release up to 7 times the amount of phosphorus and make it available for recovery in the sludge handling phase compared to a classic ASP. Based on these results, the ideal system for recovery of phosphorus and nitrogen would be a BNR process combined with a struvite recovery system. The overall evaluation of a combination of analyses concluded that shifting to a form of recovery that includes a combination of EBPR on the liquids stream followed by precipitation on the solids stream could recover a vast amount of the phosphorus coming into the treatment plant. This would not only make Central Valley Water Reclamation Facility more sustainable and efficient, but could imply an economic value as well, if phosphorus was sold to other industries. |
