Biological phosphorous removal from surface waters

Nutrient input into waterways from agriculture runoff, sewage, and other sources is a major cause of water pollution and cultural eutrophication. Nutrients such as nitrogen and phosphate are growth-limiting substrates that when present in high concentrations allow for unchecked growth of cyanobacteria. Significant cyanobacterial growth results in reduced water quality and the potential for proliferation of harmful algal blooms (HABs). Physical removal of these nutrients from waterways is needed. We seek to utilize immobilized phosphorous accumulating bacteria as a phosphate biofilter. The immobilized cells are contained in a porous, rigid container that can be suspended in a high phosphate water system and retrieved at predetermined times to collect the phosphate. Growth and PO₄ uptake was monitored in free-living pure cultures of the phosphate hyperaccumulator M. phosphovorus and other phosphate accumulators. M. phosphovorus was most effective at phosphorous uptake at a rate of 3 ppm PO₄/h (1.05 mmol P/h). Upon switching the cells to an anaerobic environment PO₄ was released at a rate of 1.75 ppm PO₄/h (0.6 mmol P/h), thus allowing control of uptake and release of PO₄ by the bacteria from the water. Encapsulated cells were found to be metabolically active even after 53 days of encapsulation, but with lower rates of phosphate uptake. Immobilized cells were introduced into high phosphate (26 ppm) aquaculture water where 12 ppm phosphate was taken up within 72 h. Repeated application of this process would allow for large-scale removal of phosphate, thus reducing the eutrophication effect and limiting the potential for HABs.