Alkaline solubilization of excess mixed sludge and the recovery of released phosphorus as magnesium ammonium phosphate.

The alkaline solubilization of excess mixed sludge was investigated and subsequently the released phosphorus was recovered as magnesium ammonium phosphate (MAP). Considerable and rapid release of glycogen and protein was encountered after alkaline addition into the sludge. Only 45.0% of sludge cells were destructed after 240 min treatment in R1 while the corresponding ratio was 96.1% in R3 according to the release of DNA. Non-apatite inorganic phosphorus (NAIP) in the alkaline treated sludge decreased due to the dissolution of Al(OH)3 and AlPO4, which was the dominant reason for phosphorus release. Soluble orthophosphate (SOP) in the supernatant of alkaline treated sludge could be recovered quickly with the recovery efficiency of 84.6% within 5 min and about 53-55% of P participated in MAP reaction, producing large amounts of acicular crystals.

[Response of Algae to Nitrogen and Phosphorus Concentration and Quantity of Pumping Water in Pumped Storage Reservoir].

Taking a pumped storage reservoir located in southern China as the research object, the paper established a three-dimensional hydrodynamic and eutrophication model of the reservoir employing EFDC (environmental fluid dynamics code) model, calibrated and verified the model using long-term hydraulic and water quality data. Based on the model results, the effects of nitrogen and phosphorus concentrations on the algae growth were analyzed, and the response of algae to nitrogen and phosphorus concentration and quantity of pumping water was also calculated. The results showed that the nitrogen and phosphorus concentrations had little limit on algae growth rate in the reservoir. In the nutrients reduction scenarios, reducing phosphorus would gain greater algae biomass reduction than reducing nitrogen. When reducing 60 percent of nitrogen, the algae biomass did not decrease, while 12.4 percent of algae biomass reduction could be gained with the same reduction ratio of phosphorus. When the reduction ratio went to 90 percent, the algae biomass decreased by 17.9 percent and 35.1 percent for nitrogen and phosphorus reduction, respectively. In the pumping water quantity regulation scenarios, the algae biomass decreased with the increasing pumping water quantity when the pumping water quantity was greater than 20 percent of the current value; when it was less than 20 percent, the algae biomass increased with the increasing pumping water quantity. The algae biomass decreased by 25.7 percent when the pumping water quantity was doubled, and increased by 38.8 percent when it decreased to 20 percent. The study could play an important role in supporting eutrophication controlling in water source area.

[Status analysis of nutrients and eutrophication assessment in Shenzhen coastal waters].

Based on the field data of Shenzhen coastal water quality in 2002-2007, variation characteristics of nutrients including NH4+ -N, NO3- -N, NO2- -N, PO4(3-) -P and DIN were presented. And the correlationships between nutrients and pH, salinity were also investigated. Furthermore, eutrophication index (E), organic pollution index (A) and potential eutrophication were employed to assess the eutrophication degree of Shenzhen coastal waters. Results show that the nutrient levels of east coast are higher than that of west coast. And the peak year of nutrients are 2002 and 2006. The average concentrations of PO4(3-) -P and DIN are 0.007 mg/L and 0.078 mg/L for Shenzhen east coast while 0.090 mg/L and 1.544 mg/L for west coast. Nutrients in Shenzhen coastal waters have negative correlations with pH and salinity. The N/P ratios are all far more than 16 indicating that Shenzhen coast belongs to seriously P-limiting water. Eutrophication degree of Shenzhen east coast is far lower than that of west coast, and the average eutrophication index of east coast is 0.11 while 42.15 for west coast. Furthermore, west coast is classified as P-limiting moderate level potential eutrophication area and even as P-limiting potential eutrophication level.