Uncontrolled discharge of ammonia in treated effluent from wastewater utilities is harmful to the receiving bodies of water. At high concentrations ammonia is toxic to aquatic life. It also adversely impacts the presence of dissolved oxygen which is critical to the health of water bodies. Additionally, discharge of nitrogen in treated wastewater in all forms, including ammonia, promotes undesirable growth of aquatic plants e.g., hyacinth, algae, etc., also called eutrophication, which renders water unsuitable for use and recreational purposes. Environmental regulators throughout North America and globally are increasingly calling for effluent nitrogen control, which requires nitrification as the first step. Nitrification involves biological oxidation of ammonium ions in wastewater. It is kinetically a very slow process and sensitive to environmental conditions, especially wastewater temperature, pH, presence of heavy metals and other toxicants. Many treatment plants, especially in rural US and Canada are lagoon based that can remove only organic pollutants - BOD (biological oxygen demand). In winter, these lagoons are exposed to very low ambient temperatures. Nitrification is difficult to sustain under cold temperatures <5
oC. Moving Bed Biofilm Reactors (MBBR) have been shown to effectively conduct nitrification under sustained low temperature conditions while consistently achieving low ammonia limits. Other benefit of the MBBR process include â (a) automatic growth and retraction of the biofilm under varying flows and loads without having the operator to adjust, monitor, or control parameters such as recycled activated sludge (RAS) and mixed-liquor suspended solids (MLSS), (b) requirement of much smaller reactor volume and footprint area, and (c) ability to quickly recover from hydraulic surges, and toxic and shock loads.
Batesville, AR, has a population of around 10,000 but its wastewater treatment plant treats 60,000 population equivalent flows due to many industrial facilities in the area including poultry and dairy industries. Prior to 2015, lagoons were used to treat the wastewater to remove only BOD. Lagoons were also used to settle the solids. Due to substantial growth in industrial discharges to the facility, the plant was stretched to the limit to remove BOD, especially in winter, when the water temperature in the lagoons reach as low as 4o C.
In 2015, the plantâs permit was revised to remove ammonia-nitrogen with a year-around limit. Due to the very low water temperatures in winter expansion of the lagoons was not considered a viable option. MBBR was selected as the technology to meet the new regulatory requirements for BOD and ammonia-nitrogen control due to its ability to perform under very low temperatures and handle varying and toxic loads from industrial contributors.
This presentation will consist of an analysis of many years of operating data demonstrating how the MBBR process helped the treatment plant achieve its goals of producing stable effluent quality consistently over the year even under low temperatures and varying loads. Operating performance will be compared with kinetic models based on the principle of MBBR technology.
