Wastewater and sludge are potential resource of phosphorus (P) for fertilizer production. One method of recovering phosphorus is via chemical precipitation. In the study, phosphorus was recovered from wastewater and sludge. First, hydrolysis was carried out to release the phosphorus in the sludge by the addition of 1.0M acid (sulfuric acid) or base (sodium hydroxide) solution mixed for three hours at 200 rpm. The hydrolyzed sludge was filtered, and the pH of the solution was adjusted to 9.0. Precipitation for both wastewater and hydrolyzed sludge solution was carried out using magnesium chloride hexahydrate (MgCl2•6H2O) and ammonium chloride (NH4Cl). The mixture was stirred for an hour for crystallization. Precipitates were allowed to settle for 24 hours before it was filtered and dried in an oven at 55-58oC for 24 hours. The dried sample was grinded and characterized using Fourier transform infrared spectroscopy (FTIR), x-ray fluorenscence (XRF), and scanning electron microscope with energy-dispersive x-ray spectroscopy(SEM-EDX).

The current effluent standards emphasize on the removal of nutrients from sewage, and one solution is for establishments to install biological nutrient removal (BNR) technologies. However, there are several factors to be considered in installing or upgrading the technologies. Hence, the study utilizes two multi-criteria decision analysis (MCDA) tools to determine the important attributes and the optimal technology from the perspective of the academe, regulatory agency, and industry. Calibrated fuzzy analytical hierarchy process (FAHP) calculates the relative importance of the three criteria (implementability, financial, and socio-environmental) and twelve sub-criteria. On the other hand, the grey relational analysis is used to calculate the performance of the four selected alternatives: 3-stage Bardenpho (A2O), 5-stage Bardenpho (5BP), sequencing batch reactor (SBR), and membrane bioreactor (MBR). Combining the results of calibrated FAHP and GRA provided the overall ranking of alternatives. Results showed that each sector prioritized different factors in the selection of the optimal BNR technology. The academe considers socio-environmental (0.43) as the most preferred criterion, while the regulatory agency and industry consider financial (0.36) and implementability (0.57), respectively. Overall, the three sectors agreed that the sequential batch reactor (SBR) is the optimal BNR technology (GRG = 0.69 - 0.79).

The study investigated the effect of storage conditions on the stability of electrolyzed seawater (ESW)’s physicochemical properties (pH, oxidation-reduction potential (ORP), and free chlorine (FC) concentration), and bactericidal efficiency on the fecal coliform Escherichia coli for 30 days. Preliminary experiments were conducted to determine the optimal current and electrolysis time. Two batches of 2750 mL filtered seawater were electrolyzed using 50 mm × 192 mm platinum–titanium mesh electrodes at a current of 1.5 A for 20 min. One hundred milliliters of electrolyzed solution was transferred into each amber glass and high-density polyethylene (HDPE) bottles. The bottles were stored in a dark area at ambient temperature. The results showed an increase in pH and a decrease in ORP and FC concentration through time. Hypochlorous acid remained as the dominant component since the pH levels of the solutions remained below 7.5. FC decay was investigated using Chick’s Law. It was determined that the decay in HDPE bottles (k = −0.066 day−1) was faster compared to amber glass bottles (k = −0.046 day−1). Nonetheless, HDPE bottles could still be used as an alternative container for 30 days only due to observed instability beyond 30 days. ESW remained effective since no surviving population of E. coli was observed throughout the experimentation.

Insufficiency of phosphorus due to the limited availability of phosphate rocks is predicted within the next decades. Phosphorus recovery from wastewater sludge was found to be one of the possible alternative sources of phosphorus. Moreover, stringent effluent standards, including that of phosphorus levels, have been newly implemented in the Philippines. Due to these factors, phosphorus recovery from wastewater in Philippine settings was deemed as an important topic to be further studied. In this paper, the feasibility of recovering phosphorus from septage sludge in Metro Manila by the precipitation of struvite crystals was studied. Septage sludge is seen as one of the potential sources and was characterized in terms of the concentration of Mg2+, Ca2+, NH4+ and PO4-3 ions. In the lab-scale experiments conducted, alkaline hydrolysis using sodium hydroxide was performed as a sludge pretreatment before the precipitation proper. Alkaline hydrolysis was done to release the remaining PO4-3 ions from the solids present in the sludge, thereby promoting precipitation after hydrolysis without the need for additional phosphate source. Furthermore, alkaline hydrolysis can effectively release phosphorus without inducing the dissolution of interfering ions such as Ca2+ and other heavy metals. Results show that PO4-3 ions increased by 267.37 mg/L and the total amount of phosphate ions increased from 17.05% to 46.88%, showing the effectivity of the hydrolysis. For the precipitation of struvite, three parameters were controlled: pH, residence time, and Mg:P ratio. After precipitation, the phosphorus recovery efficiency for the runs were each evaluated and analyzed in order to determine the effects of the parameters on phosphorus recovery. The precipitate of the run with the highest phosphorus recovery obtained was then evaluated using XRD analysis. It was found that the sample with the highest phosphorus recovery is 53.12%, which was achieved at pH 9, a residence time of 1 hour, and an Mg:P ratio of 1.5:1. Therefore, it can be concluded that precipitation subjected at pH 9 has the highest potential for higher phosphorus recovery. Further, the residence time has a minimal effect on phosphorus recovery and higher phosphorus recovery can be achieved at a higher Mg:P ratio with increasing potential for struvite recovery.

Water utilities, commercial and industrial establishments are required to upgrade or install new treatment systems to comply with the revised effluent standards issued by the Department of Environment and Natural Resources – Environment Management Bureau (DENR – EMB) which now includes removal and monitoring of nutrients (nitrogen and phosphorus components). One solution is to utilize a biological nutrient removal technology (BNRT) system capable of removing nutrients from sewage. The on-going study aims to investigate the performance of the pilot-scale system in the removal of nutrients from sewage. The designed pilot-scale anaerobic-anoxic-oxic (A2O) process with a total hydraulic retention time of 8.37 hrs. was operated in an existing sewage treatment plant (STP). System modification was adapted to ensure continuous operation. Dissolved oxygen (DO) and temperature of each compartment were evaluated after 45 days of system modification. The DO of the anaerobic and oxic compartment remained within the required range, while the internal recycling flowrate and/or aeration must be adjusted to achieve a DO concentration of 0.20 – 0.50 mg/L in the anoxic compartment. The research is financially supported by the Philippine Council for Industry, Energy and Emerging Technology Research and Development of the Department of Science and Technology (PCIEERD Project No. 04176).