Pilot Study Compares MBBR and Suspended Growth Biological Nitrogen Removal Performance for Upgrades at the Hopewell Regional Wastewater Treatment Facility

This Technical Memorandum summarizes the results and conclusions drawn from the pilot-scale testing of two segregated treatment system alternatives performed at the Hopewell Regional Wastewater Treatment Facility (HRWTF) from October 2012 through June 2013. The segregated treatment system concept for the HRWTF is intended to address the temperature issue associated with the main influent stream by achieving biological nitrogen removal on all of the domestic flow and a portion of the Honeywell flow. These two waste streams contain a substantial nitrogen load and are segregated from the stream that contains the majority of the heat load. The Honeywell flow is expected to be inhibitory to nitrification, and the process stability depends on the dilution of the Honeywell flow by the domestic flow. The two segregated treatment system alternatives pilot tested were:1. Moving Bed Biofilm Reactor (MBBR): Based on findings from the alternatives evaluation, a MBBR treatment system constructed in new tanks was recommended for the Phase 2 improvements. The resistance to spike loads of inhibitory compounds due both to the biofilm structure as well as the separate BOD oxidation and nitrification fixed film compartments made this the preferred alternative.2. Suspended Growth: A parallel suspended growth pilot system was also recommended for pilot testing to compare performance with the MBBR system and to evaluate the anticipated benefits of the MBBR system.Results from the pilot testing indicate that:• Both the MBBR and Suspended Growth processes were able to achieve comparable levels of nitrification and TN removal at the PER Design Basis of 40% Honeywell (expressed as a percent of the total Honeywell flow - equivalent to 19% of the combined influent flow including Honeywell and Domestic Primary Effluent).• The MBBR system was more stable during loading condition transitions and with higher fractions of Honeywell in the combined influent than the Suspended Growth system. The MBBR typically outperformed the Suspended Growth system with regards to ammonia, TN, and COD removal. The MBBR was able to maintain the necessary level of performance more consistently, while the Suspended Growth system performance was more variable. Overall the MBBR performance was more stable and achieved higher removal efficiencies of ammonia, TN, and COD.• Solids separation in the Suspended Growth system (clarification) was poorer than the MBBR (dissolved air flotation). In addition to the consistently higher effluent TSS from the Suspended Growth system, the clarifier also experienced floating sludge and ammonia release, particularly as temperatures increased. Although pilot clarifiers commonly perform worse than full scale clarifiers, the history of clarifier settling problems at the HRWTF makes the pilot clarifier performance an important concern. In contrast, the DAF unit piloted for the MBBR system consistently achieved lower effluent TSS than the Suspended Growth system (even without polymer addition).• It is not recommended that the segregated treatment system design basis be revised around treating a larger percentage of the total Honeywell flow stream at design minimum temperatures for the following reasons:○ The potential for sporadic upsets to nitrification was experienced even at the PER Design Basis of 40% of the total Honeywell flow at Design Average conditions (equivalent to 19% Honeywell as a percentage of the total combined influent).○ Although the systems performed well at the 70% and 100% Honeywell conditions, the pilot systems were operating above minimum design temperatures. Nitrification performance of the systems at 70% and 100% Honeywell conditions was not demonstrated at design minimum temperature (14 °C). Because nitrification rates are sensitive to operating temperatures, there are concerns that the systems would be susceptible to ammonia breakthrough and nitrification loss at the 70% and 100% Honeywell conditions at lower operating temperatures.○ The favorable performance at Honeywell loadings higher than the PER can be taken as evidence of the robustness of the process, but not as an indication that stable nitrification could be sustained at higher Honeywell loads at design minimum temperatures.