The determination of fertilizer quality of the formed struvite from effluent of a sewage sludge anaerobic digester

Optimization of struvite crystallization protocol for pretreating the swine wastewater and its impact on subsequent anaerobic biodegradation of pollutants

Higher contents of NH(4)(+) and SS in wastewater hamper the anaerobic digestion; necessitating its pretreatment to reduce them. This study reveals optimization of struvite/MAP precipitation protocol followed by anaerobic digestion of pretreated swine wastewater for pollutants removal. Levels of different treatments: stirring speeds, 400 and 160 rpm; pH values, 9.0, 9.5, 10.0, 10.5, 11.0 and 11.5; and P:Mg:N ratios, 1:1:1.2, 1:1:1.7, 1:1:2.2, 1:1:2.7, 1:1:4.0 and 1:1:5.0 were evaluated for MAP crystallization. Among various combinations, protocol comprising of initial 10 min stirring at 400 rpm followed by 160 rpm for 30 min, pH 10.0, and P:Mg:N ratio 1:1:1.2 rendered the best removal efficiency for NH(4)(+), PO(4)(3-), COD, TC and TOC. Subsequent anaerobic biodegradation revealed superiority of MAP supernatant over raw swine wastewater for methane yield and NH(4)(+)-N, PO(4)(3-)-P, COD, TC and TOC removals. It suggests that struvite precipitation as pretreatment to anaerobic digestion is highly effective and advantageous in wastewater treatment.

Laboratory experiments on simultaneous removal of K and P from synthetic and real urine for nutrient recycle by crystallization of magnesium-potassium-phosphate-hexahydrate in a draft tube and baffle reactor

The simultaneous removal of K and P from urine for nutrient recycling by crystallization of magnesium potassium phosphate hexahydrate (MPP) in a laboratory-scale draft tube and baffle reactor (DTBR) is investigated. Results show that mixing speed and hydraulic retention time are important operating factors that influence crystallization and crystal settlement. Slurry should be discharged at a crystal retention time of 11 h to maintain fluidity in the reactor. Further applications of the DTBR using real urine (pretreated by ammonia stripping and diluted five times) showed that 76% K and 68% P were recycled to multi-nutrient products. The crystals collected were characterized and confirmed mainly as a mixture of magnesium ammonium phosphate hexahydrate, MPP, and magnesium sodium phosphate heptahydrate. Results indicate that the DTBR effectively achieved the simultaneous recycling of K and P from urine to multi-nutrient products through MPP crystallization.

Utilization of municipal sewage sludge as additives for the production of eco-cement

The effects of using dried sewage sludge as additive on cement property in the process of clinker burning were investigated in this paper. The eco-cement samples were prepared by adding 0.50-15.0% of dried sewage sludge to unit raw meal, and then the mixtures were burned at 1450 °C for 2 h. The results indicated that the major components in the eco-cement clinkers were similar to those in ordinary Portland cement. Although the C(2)S phase formation increased with the increase of sewage sludge content, it was also found that the microstructure of the mixture containing 15.0% sewage sludge in raw meal was significantly different and that a larger amount of pores were distributed in the clinker. Moreover, all the eco-cement pastes had a longer initial setting time and final setting time than those of plain cement paste, which increased as the sewage sludge content in the raw meal increased. All the eco-cement pastes had lower early flexural strengths, which increased as the sewage sludge content increased, while the compressive strengths decreased slightly. However, this had no significant effect on all the strengths at later stages. Furthermore, the leaching concentrations of all the types of eco-cement clinkers met the standard of Chinese current regulatory thresholds.

Recovery of phosphorus as struvite from sewage sludge ash

Phosphorus (P) is an element vital for all living organisms, yet the world's reserves of phosphate rock are becoming depleted. This study investigated an effective P recovery method from sludge ash via struvite precipitation. Results showed that more than 95% of the total P content was extracted from sludge ash by applying 0.5 mol/L HCl at a liquid/solid ratio of 50 mL/g. Although heavy metal leaching also occurred during P extraction, cation exchange resin efficiently removed the heavy metals from the P-rich solution. Orthogonal tests showed that the optimal parameters for P precipitation as struvite would be a Mg:N:P molar ratio of 1.6:1.6:1 at pH 10.0. X-ray diffraction analysis validated the formation of struvite. Further investigations revealed that the harvested precipitate had a high struvite content (97%), high P bioavailability (94%), and low heavy metal content, which could be considered a high quality fertilizer.

Towards global phosphorus security: a systems framework for phosphorus recovery and reuse options

Human intervention in the global phosphorus cycle has mobilised nearly half a billion tonnes of the element from phosphate rock into the hydrosphere over the past half century. The resultant water pollution concerns have been the main driver for sustainable phosphorus use (including phosphorus recovery). However the emerging global challenge of phosphorus scarcity with serious implications for future food security, means phosphorus will also need to be recovered for productive reuse as a fertilizer in food production to replace increasingly scarce and more expensive phosphate rock. Through an integrated and systems framework, this paper examines the full spectrum of sustainable phosphorus recovery and reuse options (from small-scale low-cost to large-scale high-tech), facilitates integrated decision-making and identifies future opportunities and challenges for achieving global phosphorus security. Case studies are provided rather than focusing on a specific technology or process. There is no single solution to achieving a phosphorus-secure future: in addition to increasing phosphorus use efficiency, phosphorus will need to be recovered and reused from all current waste streams throughout the food production and consumption system (from human and animal excreta to food and crop wastes). There is a need for new sustainable policies, partnerships and strategic frameworks to develop renewable phosphorus fertilizer systems for farmers. Further research is also required to determine the most sustainable means in a given context for recovering phosphorus from waste streams and converting the final products into effective fertilizers, accounting for life cycle costs, resource and energy consumption, availability, farmer accessibility and pollution.

Simultaneous removal of phosphorus and potassium from synthetic urine through the precipitation of magnesium potassium phosphate hexahydrate

This study investigated the simultaneous removal of P and K from synthetic urine through the precipitation of magnesium potassium phosphate hexahydrate (MPP, MgKPO(4)·6H(2)O) in bench-scale experiments. Results show that the removal efficiencies of P and K are mainly determined by the solution pH and the molar ratio of Mg:K:P. Co-precipitation of struvite-type compounds, i.e., magnesium ammonium phosphate hexahydrate (MAP, MgNH(4)PO(4)·6H(2)O), magnesium sodium phosphate heptahydrate (MSP, MgNaPO(4)·7H(2)O), and MPP, was confirmed by analysis of the solid precipitates using a Scanning Electron Microscope/Energy Dispersive X-ray Apparatus and an X-ray Diffractometer. The co-precipitation significantly influenced the removal of K. As much ammonium as possible should be removed prior to MPP precipitation because MAP had higher tendency to form than MPP. The inevitable co-precipitation of MPP and MSP resulted in the addition of more MgCl(2)·6H(2)O and Na(2)HPO(4)·12H(2)O to obtain the high removal of K. In total, the removal efficiencies of P and K were 77% and 98%, respectively, in the absence of ammonium when pH was 10 and the molar ratio of Mg:K:P was 2:1:2. The results indicate that the MPP precipitation is an efficient method for the simultaneous removal of P and K to yield multi-nutrient products.