Water Journal : Water Journal July 2012
environmental concerns refereed paper technical features 58 JULY 2012 water Results Phosphorus adsorption The OP concentrations in the filtered secondary effluent (first column influent), the first column effluent, and the second column effluent (final) were compiled for each phase of testing. Selected figures are shown in this paper. (For a full description of all the testing results, please refer to the technical paper by Fitzpatrick et al. (2010).) Figures 4 and 5 show the results of the Phase 2 testing (diurnal loading and simulated storm flows). Online OP monitoring indicated that effluent OP concentrations consistently remained ultra-low during all phases, while the influent OP concentration varied from 0.2 to 5.0 mg-P/L. Results of the laboratory analyses of daily composite samples agreed favourably with the online measurements. Phosphorus desorption and recovery An alkaline solution was used to desorb the phosphorus from the media. Lime was later added to the desorption solution to precipitate the phosphorus as calcium phosphate and the precipitated solids were subsequently dewatered. The filtrate from each recovery cycle was captured and reused as desorption fluid in subsequent cycles. The recovered solids (Figure 6) from multiple recovery cycles were collected and sampled multiple times during the testing phases, and sent to a commercial laboratory for nutrient and metal analyses. Table 2 summarises the quality of the recovered solids from the Lawrence pilot testing, together with the maximum allowable concentrations established by national and state regulatory agencies in North America, Europe, and Asia Pacific. Compared to phosphate rock, the recovered solids had a very low cadmium concentration (the primary metal of concern for phosphorus fertilisers). Previous pilot testing in Japan found very low levels for other metals of concern. The phosphorus content of the filter cake compared favourably to the 28% P2O5 minimum normally stipulated by fertiliser manufacturers. Conclusions and Recommendations The Lawrence pilot testing of the intergrated phosphorus adsorption and recovery system demonstrated the capability of this technology to achieve ultra-low phosphorus concentrations and recover the phosphorus as a high-grade fertiliser. The high selectivity of the media to phosphate ions compared to other ions in the effluent is one of the main reasons for the efficiency of this recovery process. This unique ability to adsorb phosphate almost exclusively also explains the high phosphorus content of the recovered solids and may also partly explain their low metal content. Further optimisation of the recovery process, particularly the neutralisation steps, may help to further reduce chemical usage. Such optimisation is expected to be somewhat site-specific based upon the unique influent Figure 4. Influent and treated effluent orthophosphate concentrations during Phase 2 testing. Figure 5. Cumulative P calculated for each adsorption cycle during Phase 2 testing. Figure 6. Recovered solids from the Lawrence pilot.
Water Journal August 2012
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