Extraction of nutrients from foam in a membrane activated sludge system

Abstract

This study investigated the feasibility of treating the foams generated in enhanced biological phosphorus removal processes with the microwave-enhanced advanced oxidation process to reduce solids and solubilize nutrients for recovery purposes. It was found that more than half of the total chemical oxygen demand was solubilized during the treatment with just a small dose of hydrogen peroxide, signifying effective destruction of foam solids. Significant solubilization of phosphates, volatile fatty acids and ammonia was also observed, along with the release of metals contained in the foam, including calcium, potassium, and magnesium, which thereby represents additional potential benefits for nutrient recovery via subsequent crystallization processes. Since the solids content of foam is typically high, pretreatment for thickening sludge solids is not necessary prior to the use of microwave-enhanced advanced oxidation processes. As a result, this also offers further potential for reduction of energy costs. The process could be an efficient method for the removal and control of foam and the recovery of all available phosphorus at the same time.

Nutrient recovery from foam with microwave treatment

“…The R 2 value for VFA screening model was 0·93 indicating a good fit. Similar results were observed during studies on foam and sewage sludge after MW/H 2 O 2 -AOP treatment Lo et al, 2010). In a real-time MEBPR operation, VFAs obtained from MW/H 2 O 2 -AOP treated foam could be recirculated to front end of the plant as a carbon source for bio-P process.…”

“…Additionally, MW/H 2 O 2 -AOP treatment of foam exhibited seven times more solids disintegration in terms of total chemical oxygen demand (TCOD) than treated mixed liquor (Hall et al, 2011;Lo et al, 2010). Therefore, foam can be a better suitable substrate than sludge for MW process and a resource, instead of being a nuisance, by recovering nutrients and reducing solids handling burden in WWTP.…”

“…Control experiment results and results from the earlier studies clearly indicated the importance of hydrogen peroxide addition to improve nutrient release and solubilisation of carbonaceous matter Lo et al, 2010). Therefore, hydrogen peroxide dosage was chosen to be important variable in the RSM experimental design.…”

“…Microwave treatment was applied with the closed-vessel MW digestion system (Ethos TC Digestion Lab station 5000, Milestone Inc., USA) with an operating frequency of 2450MHz and a maximum power supply of 1000W (Kenge et al, 2009;Lo et al, 2010). To accommodate pressure built up at high operating temperature in a closed vessel system, the weight of each foam sample was maintained to 30g in each set of experiments.…”

“…So far, nutrient recovery potential from foam has not been explored in detail. Lo et al (2010) studied the MW/H 2 O 2 -AOP treatment of foam at relatively lower temperature with (pH ∼2) and without pH adjustment. Such studies on MW/H 2 O 2 -AOP treatment of foam were conducted when the SRT at MEBPR was as low as 10d; however, during recent operations, the SRT has been increased to as high as 25d.…”