Water Online the Magazine gives Water & Wastewater Engineers and end-users a venue to find project solutions and source valuable product information. We aim to educate the engineering and operations community on important issues and trends.
Issue link: http://wateronline.epubxp.com/i/164223
Case Study Filamentous Bacteria Controlled: A Quick And Easy Solution The City of Kalispell used ingenuity, and just a few inexpensive parts, to solve a problem common to biological nutrient removal facilities. By Rebecca Bodnar F food source, fatty acids, is difficult ilamentous foaming bacto accomplish while maintaining Left unresolved, filamentous teria: the nuisance of phosphorus removal; lowering many biological nutrient bacteria can reduce clarifier removal (BNR) wastewa- capacity, cause digester foaming, the SRT reduces sludge-handling capability and interferes with both ter treatment plants. Although and carry over to effluent. phosphorus and nitrogen removal; filamentous microorganisms are and surface wasting can be labora natural part of the biomass in intensive. During the overproliferation of the filaments, the plants and are the backbone of floc formation and setKalispell WWTP operators employed these methods, but the tling, the overproliferation of filamentous microorganisms foam continued to accumulate. causes the sludge to float (foaming) and causes problems with nitrification and phosphorus removal, aesthetics, Ingenuity To The Rescue poor settling, and the formation of high-sludge blankets. Chlorine and hydrogen peroxide have been used successLeft unresolved, filamentous bacteria can reduce clarifully to selectively kill filamentous bacteria.3 Chlorine is the fier capacity, cause digester foaming, and carry over to most widely used toxicant, as it is relatively inexpensive and effluent. The City of Kalispell (MT) Advanced Wastewater readily available. A highly concentrated chlorine solution (0.5 Treatment Plant (WWTP) upgraded in 2007 to a Modified to 1.0 percent) has been shown to be successful.4 A Kalispell Johannesburg configuration for phosphorus and nitrogen WWTP operator, Aaron Losing, brainstormed an idea to utiremoval. Seasonally in spring, filamentous bacteria growth lize an existing spray system to efficiently and cost-effectively consistently rises sharply and becomes a problem in the spray the foam with chlorine. During the plant's original conaeration basins. A huge amount of floating sludge accustruction in 1992, the engineering staff foresaw the potential mulates in the tanks, and removal of the floating layer is a for foaming and equipped each individual biocell in the plant serious problem. bioreactor with a spray bar across the width of the cell. The plant utilizes nonpotable effluent to physically move or push Tried, Not True the foam out the biocells and Three filamentous organisms can into a collection channel at the cause activated sludge foaming: end of the bioreactor for surface Nocardia sp. (most common), wasting. This system worked well Microthrix parvicella (less com1,2 until the plant was upgraded in mon), and Type 1863 (rare). 2007 to the current configuration. The more common foamAfter 2007, the system did not causing filaments, Nocardia remove enough of the filamenand M. parvicella, both favor tous microorganisms, and the BNR plant characteristics: long removal process became increassolids retention times (SRTs), ingly labor-intensive. However, alternating aerated/nonaerated the existing spray bar system zones, foam-trapping environcreated an excellent starting point ments, and fatty acids as a food for the addition of chlorine spray source. Many control measures for foam control. exist, including eliminating food Three-inch chlorinatsources, lower SRT, and suring dosing tablets (found at face wasting. These measures all Simple methods resolved sludge foaming at the Kalispell WWTP, pictured here. pool maintenance stores) are have drawbacks. Eliminating the 36 wateronline.com ■ Water Online The Magazine