Enhanced Coagulation is a new regulatory requirement in the United States aimed at removing TOC by coagulation thereby controlling formation of disinfection byproducts. Coagulation principles are summarized for alum coagulation of natural organic matter (NOM). Negatively charged NOM creates a coagulant demand for positively charged Al species resulting in a stoichiometric relationship between the alum dosage and the raw water DOC that is pH dependent. The paper addresses coagulation with a broader view than Enhanced Coagulation, termed multiple objective coagulation. In general the objectives include: 1) to maximize particle and turbidity removals by downstream solid-liquid separation, 2) to maximize TOC and DBP precursor removals, 3) to minimize residual coagulant, 4) to minimize sludge production, and 5) to minimize operating costs. Optimum coagulation conditions are those that maximize pathogen removals, produce low turbidities and particle counts, and minimize residual Al. It is shown, for treatment of waters of low alkalinity, that the optimum alum dosage selected to minimize UV absorbance with strict pH control produced excellent treatment for turbidity, pathogens, and NOM. Full scale plant data are used to demonstrate a dual coagulation strategy of alum and cationic polymer that reduces sludge production and overall operating costs compared to alum alone.

Manganese (Mn) in drinking water can cause aesthetic and operational problems. Mn removal is necessary and often has major implications for treatment train design. This review provides an introduction to Mn occurrence and summarizes historic and recent research on removal mechanisms practiced in drinking water treatment. Manganese is removed by physical, chemical, and biological processes or by a combination of these methods. Although physical and chemical removal processes have been studied for decades, knowledge gaps still exist. The discovery of undesirable by-products when certain oxidants are used in treatment has impacted physical-chemical Mn removal methods. Understanding of the microorganisms present in systems that practice biological Mn removal has increased in the last decade as molecular methods have become more sophisticated, resulting in increasing use of biofiltration for Mn removal. The choice of Mn removal method is very much impacted by overall water chemistry and co-contaminants and must be integrated into the overall water treatment facility design and operation.

The objectives of this work were to include chemical effects in the fundamental theories that describe the deposition of particles in granular media filters, to test the theories experimentally, and to use these results in assessing requirements for effective filtration and the capabilities of the process. In particular, the effects of changes in solution chemistry on the deposition of relatively large or non-Brownian particles are examined. Such particles are large enough, typically with diameters greater than 2-3 pm, that their transport is not significantly affected by Brownian diffusion.JOURNAL AWWA

Arsenic sorption to hydrous ferric oxide (HFO) is an effective treatment method for removing dissolved arsenic from fresh drinking water sources. However, detailed information is limited regarding arsenic removal from solutions of high ionic strength such as brackish groundwater, seawater, or high-pressure membrane process residuals. Bench-scale treatment experiments were conducted exploring arsenic removal from simple solutions with ionic strengths ranging from 0.008 to 1.5 M by addition of ferric chloride followed by solid/liquid separation (microfiltration or ultrafiltration). Arsenic removal from these solutions during in situ iron precipitation was approximately 90% at Fe:As molar ratios of 10 to 15 and > 95% for Fe:As molar ratios greater than 20. Arsenic removal at iron doses of 10(-6) to 10(-4) mol-Fe/L improved when pH was lowered from 8 to less than 6.5 at ionic strength 0.2 M; this improvement was not as significant at ionic strength 0.7 M. Arsenic removal diminished when alkalinity was increased from 400 to 1,400 mg/L as calcium carbonate; however, arsenic removal at the higher alkalinity improved when pH was lowered from approximately 8 to less than 7. Arsenic removal with preformed HFO solids and subsequent microfiltration was significantly less than that observed with in situ HFO precipitation. Increased removal by in situ precipitation compared to that of preformed solids is explained by an increased number of adsorption sites due to uptake during iron oxy-hydroxide polymerization as well as an increase in surface area resulting in diminished surface charge effects. Model simulations of arsenic uptake by in situ precipitation adequately captured these effect by changing the model parameters used to model arsenic uptake by preformed HFO, specificallythe total number of surface sites and surface area.