Phosphorous in Wastewater. Wastewater can be rich in carbon, nitrogen, and phosphorous contaminants which are essential nutrients for the growth of organisms. Phosphorus bans on detergents have served to reduce the levels of phosphorous in domestic wastewater. However, many industrial and food process waste streams are inherently high in phosphorous content. The discharge of a phosphorous-rich wastewater into a receiving stream may stimulate accelerated algal growth, resulting in oxygen depletion and stream eutrophication.

P Removal Methods. Traditional methods to remove solids, such as settling, filtration, and centrifuging, will remove a majority of insoluble phosphorous (P) species. Removal of the remaining soluble P has been performed in numerous ways. Under certain conditions, phosphate-accumulating microorganisms can incorporate P into their cell mass. Unfortunately, this P removal method fails when the P content is high and the nutrient ratios are less than optimal.

Other common phosphorous removal methods involve the formation of insoluble phosphate salts with aluminum or iron salts. The use of alum (aluminum sulfate) or ferric chloride for P removal has a significant drawback relating to the acidity of the coagulants that are added to the wastewater. Since both alum and ferric chloride are quite acidic in nature, they result in a decreased pH to both the settled solids as well as the effluent stream. By decreasing the pH, microbial activity in a secondary treatment system such as a digester (aerobic or anaerobic) or in other secondary treatment processes will be diminished. In addition, these coagulants tend to form highly voluminous sludge incorporating a significant percentage of water. This in turn results in increased solids handling and hauling costs.

A new method being discussed for P removal from wastewater involves the directed formation of struvite, an insoluble magnesium ammonium phosphate salt. Struvite formation in wastewater treatment plants is a relatively common but usually undesirable phenomenon, which commonly results in the clogging of wastewater pipes in areas of high flow velocity. This new approach requires the addition of new solids separation equipment a large capital investment in less than fully proven technology. More importantly, this approach can require modifications that will adversely affect the primary or secondary treatment processes in order to optimize the Mg, NH3, and P ratios for tertiary struvite formation and removal.

P Removal with an Alkalinity Boost! IER’s patent pending approach to wastewater P removal is an extension of the chemistry of the antacids used every day in human digestive systems. IER’s innovative Amalgam technology begins with a family of proprietary formulations that contain specialty blends of aluminum and magnesium additives which serve to fix the soluble P into an insoluble metal salt compound under alkaline conditions. This results in optimized total P removal within the primary clarifier solids fraction. Just like Rolaids or Tums, IER’s Amalgam formulations rely on the gentle buffering nature of magnesium hydroxide (Milk of Magnesia) and the strong coagulation benefits of aluminum hydroxide. Amalgam formulations do not just optimize the removal of soluble phosphorous, but also provide significant reductions in total suspended solids (TSS) as well as biological oxygen demand (BOD). In many cases fats, oils, and greases (FOG), and total Kjedahl nitrogen (TKN) are also significantly reduced.

By combining magnesium and aluminum into a single alkaline formulation, the benefits of each metal are fully realized resulting in optimized wastewater coagulation as well as alkalinity buffering. Aluminum cations (Al3+) provide the primary coagulation benefit, through the formation of the insoluble, polymeric, web-like structure of aluminum hydroxide, and through the formation of insoluble aluminum hydroxyphosphate. This resulting compound captures phosphorous within the solids fraction of the sludge. Magnesium ions (Mg2+) in turn aid in the minimization of the resulting sludge volume by bonding to organic solids and causing them to settle without the associated troublesome high water content. By minimizing the amount of entrapped water in the sludge matrix, the volume of the sludge is minimized and the sludge density is maximized, compared with straight iron-based or aluminum-based coagulants. This attribute of magnesium can result in a great reduction in the overall volume of sludge requiring disposal from a wastewater treatment facility.

The ratio of the aluminum-based additive and magnesium-based additive in the Amalgam composition is dependent upon the nature of the wastewater to be treated. When the primary goal of the treatment is rapid solids settling, the composition will be more predominant toward the aluminum-based additive. When the primary goal of the treatment is solids compaction or pH buffering, the composition will be more predominant toward the magnesium-based additive. The table below provides examples of the P removal performance of varying Amalgam formulations applied to the influent wastewater to a clarifier at a food processing plant.