No abstract

Research was undertaken to determine the potential for changes in GHG emissions based on the magnitude of aeration, as enhanced by the need for mixing and shearing biofilm (to manage the biofilm thickness), the type of media (fixed bed versus moving bed), and the location of media in IFAS systems. The information was used to verify the biofilm and IFAS components of the Aquifas + simulator. The simulator was developed with a proprietary algorithm that can achieve speeds greater than 100 times that of other commercial biofilm models, while solving twice as many equations for the biofilm to accommodate GHG simulations. The proprietary elements of the algorithm modify the Newton Raphson method for solving equations and the Euler method for row reduction during matrix inversion in a manner that achieves substantially higher speeds and computational accuracy. The nitrification and denitrification reactions are broken up into four steps each to simulate nitrous oxide, nitric oxide, nitrite and nitrate forms of nitrogen. The oxidized nitrogen products with reactions where both ordinary heterotrophs (OHO), polyphosphate accumulating organisms (PAO) can consume them. This expanded the activated sludge component of IWA-ASM2d from 19 to 54 equations, and the biofilm component from 19 to 34 equations.As part of this research, it was determined that an IFAS system could denitrify better with the biofilm added to the anoxic cell, and the denitrification flux (oxidized-N reduction inside biofilms, especially in thicker biofilms) creates a lower potential for emitting GHG as nitrous oxides in the anoxic zone. The simulator was applied to evaluate and conclude that the higher buffer on air supply in IFAS that is created when the aeration requirements have to satisfy the need for media mixing to shear the biofilm helps achieve more complete nitrification, thereby lowering the potential for GHG emissions. Dynamic simulation with the higher aeration and mixing shows that the more complete nitrification that can be achieved with the additional air and media in a properly designed IFAS system can also reduce the emission of nitrous oxides from the aerobic zone during peak flow periods.

Biological nutrient removal (BNR) is being selected as the cost effective option for enhancing nutrient removal at plants located in temperate climates in the Chesapeake Bay Watershed and the Long Island Sound in the U.S.A. However, there is considerable discrepancy in the reported values for temperature sensitivity for nitrification and denitrification rates in winter, as observed at different plants and those reported in higher strength wastewaters in Europe and South Africa. Full scale data show that the temperature sensitivity for nitrification is considerably lower. Denitrification rates in the primary anoxic zone are also lower, possibly because of lower influent strengths (250 to 450 mg/L COD). Secondary clarifier limitations have been a key cost factor in attempting year round nitrogen removal as against seasonal (summer) nitrogen removal. The anoxic MCRT and anoxic volume requirements have been a critical cost factor in designs. Split flow designs, where a fraction of the influent flow is sent directly to the anoxic zone, have allowed process designs with lower anaerobic volumes. The readily available COD in the fraction of the influent which enters the primary anoxic zone enhances denitrification rates. Though the anaerobic cell receives less than 100 percent of the influent flow, excellent biological phosphorus removal can still be maintained with phosphate detergent ban wastewaters. The fraction of biomass maintained under anaerobic conditions (and the anaerobic volume) can be reduced because the phosphate detergent ban has decreased the amount of phosphorus which has to be removed for the same influent COD. Biofilm and suspended growth systems have been combined in a single reactor to reduce volume requirements for nitrogen removal.

No abstract

Lake Simcoe is the second largest lake in Southern Ontario, Canada and plays an important role in the surrounding area. The 76 ML/d (20.1 mgd) Barrie Water Pollution Control Centre (WPCC), discharges to Lake Simcoe and will be required to meet strict effluent phosphorus load limits set forth by the Lake Simcoe Phosphorus Reduction Strategy. The strategy imposes annual mass load limits on the effluent total phosphorus (TP) that become increasingly more stringent in the future. Depending on the design capacity of the Barrie WPCC, the TP limit can vary from 0.04 mg/L to ultimately 0.02 mg/L. The purpose of the project is to identify the most reliable and cost effective technology to achieve the required effluent TP limits.A total of seven different types of treatment technologies were evaluated during a preliminary and detailed screening of alternatives. The technologies which were considered included Aqua Aerobic AquaDiamond® Cloth Filters, IDI Densadeg and Kruger Actiflo high-rate flocculated settling systems, CoMag ® High Rate Ballasted Settling Process, Parkson D2 ® Continuously Backwashing Upflow Sand Filters (CBSFs), Blue Pro ® (CBSFs) Filters and Tertiary Membrane Filtration. Based on the detailed evaluation of the phosphorus removal technologies, the City selected a tertiary membrane filtration system for the Barrie WPCC. Due to the difficulty of consistently achieving an effluent TP concentration at or below 0.05 mg/L, the City completed a low-level phosphorus removal pilot study utilizing a single membrane supplier. The objectives of the pilot study were to evaluate the phosphorus removal capabilities, the coagulant dose requirements and the impact to pH and alkalinity, and the solids generated. During the study, which was completed in December 2011, both alum and ferric were tested and the membranes were challenged tested with increased flow and phosphorus loads. This paper will present a brief discussion of the alternative technologies evaluated and the reason for selecting membranes and then focus on the results of the pilot tests and the lessons learned.