Browsing by Author "Thomas, David J. L."

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    Maximising struvite recovery from real wastewater sources
    (2007-04) Thomas, David J. L.; Parsons, Simon
    Formation of struvite (MgNFLjPCU.ôFfeO) in reactors is proposed to limit struvite problems in sewage treatment works (STW) and offer a method of phosphorus recovery and recycling. Four sites of interest were identified by Severn Trent Water Ltd: Derby, Wanlip, Stoke Bardolph STW and Coleshill sludge destruction plant for their potential to produce struvite. Initial tests on sludge liquors collected from the four sites showed that >80% of initial orthophosphate could be removed when the Mg:PC>4 ratios was adjusted to >2:1 for Wanlip, Stoke Bardolph STW and Coleshill at pH 9. Two reactor types, a fluidised bed reactor (FBR) and a stirred tank reactor, were trialled in Phase 1 testing with Wanlip STW liquors. The FBR was able to achieve a >90% orthophosphate removal with Mg additions of 3.5 to 5 mmol but produced a suspended solid content of -300 mg L"1. To overcome the problem of ‘fines’ a metallic mesh accumulation device was fitted to the reactor. The mesh system was able to reduce the suspended solids within the liquors <50mg L' 1 when the reaction time was increased from two to three hours. The stirred tank reactor was able to remove on average 55% of the phosphate content of the liquors with a magnesium addition of 5mmol. In Phase 2 testing both types of reactor were run side-by-side in a continuous operation. In the three experiments carried out the initial orthophosphate concentration was adjusted to 95 mg L' 1 (Immol). The stirred tank reactor was able to consistently remove -65% of the influent orthophosphate concentration in the 3 experiments at a Mg:P0 4 ratio of 3.5:1. The FBR removal steadily improved from 25% to 65% over the 3 experiments. The metallic mesh system was further trialled here and successfully captured 4.1 g of struvite. A cationic polymer, polyDADMAC, was also tested for the capture of fines with less success than in previous reports. The precipitate from each reactor was analysed with SEM-EDS and XRD. The FBR produced relatively pure struvite and stirred tank a struvite and amorphous material mixture.
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    Understanding the causes of toxicity in treated landfill leachate through whole eefluent testing
    (Cranfield University, 2010-08) Thomas, David J. L.; Tyrrel, Sean
    Landfill leachate is collected and treated before discharge to protect the environment from a potential toxic cocktail of substances. In the U.K. biological treatment is the favourite technology for rendering landfill leachate safe due its simple design, effective handling of varying chemical loads and relatively low operating costs. Biological treatment is effective at reducing the concentrations of ammoniacal-nitrogen and the biological oxygen demand (BOD) to acceptable levels for discharge. Even though the ammoniacal-nitrogen and BOD levels have been reduced there still remains a considerable quantity of refractory organic chemicals and inorganic ions. Heavy metals tend be present in very low concentrations. A view has developed that these effluents potentially pose a risk to the aquatic environment due to the presence of these compounds. Cont/d.