Nutrient recovery and management in full scale wastewater treatment plants: Feasibility and optimization.

摘要

Recovering and recycling nutrients from wastes has been a major research component in environmental engineering over the past 20 years. Advanced industrial technologies followed by excess human consumption lead to the release of higher concentrations of reactive organic and inorganic nutrients to surface water bodies leading to major environmental concerns such as eutrophication, algal blooms, etc. (Edwards et al., 2000). Besides, large amounts of nutrients present in waste streams pose a critical problem with regards to wasting and depletion of phosphorous at a significant rate. As municipal wastewater treatment plants (WWTPs) are one of the potential sites of nutrient deposition, recovering and recycling excess nutrients and closing the nutrient loop that would otherwise be discarded offers economic as well as environmental benefits. Furthermore, the depletion of natural phosphorous resources and the implementation of much stringent regulations are becoming major issues for many WWTPs and are currently emphasizing nutrient recovery and management.;In this study a series of bench top experiments were conducted to recover nutrients through chemical precipitation. Local municipal wastewater treatment plants were considered as model systems for this study. For one set of samples, nutrient recovery was tested for addition of different chemicals (i.e., sodium hydroxide (NaOH), magnesium hydroxide (Mg(OH)2), magnesium chloride (MgCl2)) at a controlled pH ranging from 8--10 to recover them in the form of struvite. For the other set of samples, effect of pH and temperature were studied on struvite recovery. In addition, to compare the recovery of nutrients in a wide range, samples were collected from diverse WWTPs containing different treatment technologies (i.e., trickling filter process, trickling filter/solids contact (TF/SC) process and enhanced biological phosphorous removal (EBPR)). Samples were collected at different times of the year to account for the varied seasonal changes and the working conditions at the WWTPs. Proportions of chemicals added and the pH maintained were optimized for each sample to achieve maximum recovery. Up to 85--90% of phosphorous and 25% of nitrogen recovery has been observed in the experiments, performed under different conditions. Maximum recovery was observed at a ratio of NH 4:PO43-+:Mg+2 1:1:2 to 1:1:1.3. Among all the samples tested, filtrate samples had the highest nutrient recovery potential.