Nutrient Whack-a-Mole - Sidestream nutrient control and assessment of the fate of sulfur, iron, and phosphorus

摘要

The biological processes utilized in wastewater treatment exhibit complex biological and chemical sulfur transformations. Despite the importance of these interactions, the impact of these transformations could not be previously explored with process modelling as the majority of biokinetic matrices did not include related reactions. Recent developments in whole plant process simulators (Hauduc et al., 2017), and modifications to the anaerobic digestion model (ADM) (Flores-Alsina et al, 2016) have allowed for the assessment of the impact of sulfur transformations. The purpose of this study is to begin to understand the interactions between sulfur, iron, and phosphorus at the Trinity River Authority of Texas' Central Regional Wastewater System treatment plant that will occur with the commissioning of the solids stabilization improvements, which include the implementation of the thermal hydrolysis process, anaerobic digestion, and iron addition for struvite mitigation. Specifically, the analysis focused on the impact of ferric chloride dosing on the formation of nuisance struvite, digester pH, gaseous hydrogen sulfide production, sidestream phosphorus loads, and the characterization of the fate of sulfur, phosphorus, and iron. Process simulations were completed using Dynamita's Sumo© version 143 at ferric doses between 0 and 7,300 kilograms ferric per day. Initial simulations predict that the addition iron first acts to oxidize dissolved sulfide constituents, reducing biogas hydrogen sulfide content, and precipitates available phosphates as vivianite. The addition of ferric chloride is not predicted to have a measurable impact on struvite formation in the digesters at moderate dosing rates. Noticeable reductions in struvite are not predicted until all available phosphate has been precipitated and enough iron exits to overcome the struvite precipitative driving forces. However, increasing doses of ferric is predicted to reduce the soluble phosphorus concentration in the biosolids. By reducing this soluble phosphorus concentration in the digester and biosolids, sidestream phosphorus loading on the liquids process will be reduced. In addition, lower soluble phosphorus concentrations should lower the risk of detrimental struvite formation on the downstream dewatering equipment.