Introduction and Problem Statement
Lagoon wastewater treatment systems employ a combination of physical, chemical, and biological processes to treat wastewater. Lagoon wastewater treatment systems are simple, natural, energy efficient, and one of the most cost effective treatment options, especially for small and rural communities. Lagoon systems are easy to operate, require lower maintenance costs, are effective in handling shock loadings and removing pathogenic organisms. Despite these benefits, lagoon treatment processes are less efficient in cold weather, ineffective at removing heavy metals, and often run into problems associated with nuisance odor and algae blooms. Therefore, proper maintenance and operation is essential for the bacteriological mechanisms to provide efficient wastewater treatment. The City of Spring Valley, II has utilized a lagoon system to treat wastewater generated by city for over 40 years. The lagoon was near capacity with approximately 91,000 cubic yards (CY) of sludge (17.8% volatile solids) due to ineffective microbiological activity. The sludge blanket contained layers of silt and sludge, which was very thick and experiencing accelerated algae growth. These factors contributed to effluent suspended solids violations and required the Environmental Protection Agency (EPA) to recommend corrective action. The City planed to dredge the lagoon, but removing the large sludge volume was cost prohibitive. Seeking alternative methods to reduce the lagoon sludge, the city requested proposals for a bioaugmentation treatment technology to reduce the economic burden of sludge disposal and to evaluate the possibility of restoring the microbiological activity in the lagoon. Through a competitive process, the City selected In-Pipe Technology (IPT) Company for 180 days of treatment to accelerate volatile solids reduction and decrease the total volatile solids volume by a minimum of 25%. IPT adds a highly concentrated formulation of robust and sustainable facultative bacteria using a low energy mixer to accelerate volatile solids reduction.
Goal and Objectives
The main goal of this project was to reduce the economic burden of sludge disposal by degrading the volatile suspended solids present in the sludge. An additional objective was to restore the microbiological activity in the lagoon so that city could operate lagoon wastewater treatment efficiently without dredging the lagoon while meeting the effluent discharge limits.
Materials and Methods
The City of Spring Valley, IL wastewater treatment lagoon receives primary clarifier effluent (-0.97 MGD) with approximately 100 mg/L of biochemical oxygen demand (BOD5) and approximately 100 mg/L of total suspended solid (TSS). The lagoon is aerated with coarse bubble diffused air headers spaced 100 feet apart throughout the entire lagoon. The effluent BOD5 and TSS discharge limit is 25 mg/L and 30 mg/L, respectively. The 14 acre lagoon is 1,200 ft long and almost 600 ft wide with a design depth of 10 ft. The current sludge depth averages 4 ft.
In-Pipe treatment strategy:
Since the lagoon wastewater treatment system is over 40 years old and had different strata of silt/sludge, IPT added a low energy (1.6 HP) floating mixer to break the strata, mix the densely packed sludge, promote oxygen transfer, and to promote contact between food and microbes (Figure 1A). The mixer provides a mixing radius of ten times the available depth, which is approximately 100 ft in diameter at Spring Valley. The mixing model is shown in Figure IB. IPT installed three automatic microbial dosing panels on the top of the floating mixer (Figure 1C). These automatic dosing panels continuously dispense microbial formulation while mixing takes place. The mixer was moved within the lagoon in accordance with an engineered plan at 200 ft increments to cycle twice around the lagoon in 180 days. Additionally, IPT added six panels at the entrance of the lagoon wastewater treatment system to inoculate the lagoon influent with a high concentration formulation of robust and sustainable facultative bacteria. Bacteria and mixing was conducted continuously from project inception.
Laboratory biochemical analysis of 8 point grid lagoon samples (% volatile solid/total solid (VS/TS), pH and NH3 concentration) were carried out by an independent contractor, Test Inc., (www.testinc.com) hired by the City of Spring Valley. The sludge blanket was too thick to measure using a sludge judge, so McClure Engineering (Engineering Consultant to the City of Spring Valley) created a topographic map of the sludge blanket using an adapted approach. In this method, a PVC disk (1/4 inch thick and 8-12 inch in diameter, specific gravity 1.4) sinks through the liquid and settles at the water-sludge interface and measures the depth from the
liquid surface to the top of the sludge layer. Sludge depth was calculated from the known depth from the liquid surface to the lagoon bottom. Each location was plotted using GPS and the sludge measurements were carried out at 50ft increments (creating a 50x50 grid). The average sludge layer depth was used in the sludge volume calculation.
A “Pre-IPT” analysis completed in December 2011 was used as a baseline to compare with IPT bioaugmentation performance. IPT Performance evaluations were carried out at the end of 180 days of IPT treatment.
Results & Discussion
Performance evaluation at the end of 180 days of low energy mixer assisted bioaugmentation treatment showed that that the volatile solids content was reduced by ~25% from 16,208 CY to 12,208 CY (Table 1). The decrease in volatile solids content is the result of enhanced contact between organics and microbes, the metabolism of the IPT bacteria (e.g., organic consumption rate, growth rate), and hydrolysis and solubilization of the complex, less biodegradable and slowly hydrolysable organics. The pH with IPT treatment (pH 7.53) did not change significantly compared to the baseline pH of 7.05. The increased in NH3 oxidation [~9% reduction (1,691 mg NH3/kg TS to 1540 mg NH3/kg TS)] is an indication of the restoration of the bacteriological activity (e.g., autotrophic and heterotrophic nitrification) with IPT bioaugmentation treatment.
IPT bioaugmentation treatment successfully reduced ~25% of the volatile solids in 180 days of treatment application and reduced City’s economic burden of sludge disposal. Additionally IPT bioaugmentation treatment restored the microbiological activity which enables the City to operate the lagoon wastewater treatment efficiently for longer periods without dredging the lagoon and while meeting the effluent discharge limit. The innovative low energy mixer assisted bioaugmentation treatment enhanced contact between bacteria and organics, improved wastewater treatment performance, and may replace traditional aeration processes.
WEFTEC’ 2013 Lagoon wastewater treatment using Innovative bioaugmentation technology case study
Introduction and Problem Statement