Innovations in Biogas Management: Overcoming Challenges in the Anaerobic Lagoon Startup in South Sioux City

The City of South Sioux City (SSC), Nebraska, faced a pivotal challenge in wastewater management when the Sioux City, IA Wastewater Treatment Plant (SCWWTP) announced its decision to cease acceptance of wastewater from local heavy industries (e.g., meat packing) . This was compounded by significant flooding in 2019 that damaged local infrastructure, prompted the city to accelerate plans for constructing its own wastewater treatment facility (WWTF). Anaerobic treatment is an ideal fit for high strength wastewaters, and with anaerobic systems comes the need for biogas handling. The City of SSC planned to utilize this resource beneficially, however sulfur quickly became a problem. The City of SSC embarked on constructing a covered anaerobic lagoon (CAL) system integrated with Nebraska's first Aerobic Granular Sludge (AGS) system to effectively manage its industrial wastewater. A site layout illustrated in (Figure 1). The lagoons where to provide pretreatment to the high strength wastewater. Lagoon discharge would then be collected in a wet well and pumped to an aerobic granular sludge system for final treatment, UV disinfection, then finally sent to the Missouri River. The anaerobic pretreatment would generate biogas that could be used beneficially in the WWTF boilers, with future plans to augment the City's natural gas by cleaning the biogas to a renewable natural gas level for injection. During the startup phase of the anaerobic lagoon, biogas was generated with unexpectedly high levels of hydrogen sulfide (H2S), reaching concentrations as high as 2.5% by volume, shown in (Figure 2). These elevated H2S levels overwhelmed the biogas H2S removal system, which utilized a proprietary activated carbon vessel designed to manage lower concentrations. The initial biogas management strategy intended for this gas was to supplement natural gas in a boiler system for heating the anaerobic lagoons, but the challenges presented by the high H2S levels made the biogas unusable in the boilers without a removal system capable of treatment. This led to the question of 'where is the sulfur coming from?'. The background water quality in the area was known to have a high sulfate concentration, and the industries were known to discharge elevated sulfur, however these two sources could only account for approximately 50% of the Sulfur coming into the facility. A sulfur balance was performed, and modeling was done to estimate the fate of the sulfur once it entered the WWTF. A simplified figure shows this balance in (Figure 3). The results lead to discussions with local industries, and the discovery of increased sulfuric acid usage at the industries on site pretreatment to meet the Cities new WWTF's influent FOG limits. HDR worked with the City, the industry, and the Nebraska Department of Environment and Energy to implement a pilot study at the industries pretreatment system. The intent was to reduce sulfuric acid usage to find a reasonable balance between acid usage and FOG discharge limits. Although the results of the pilot study succeeded in reducing sulfur to the WWTF it consequently generated colloidal none settling solids. These colloidal solids were not removed in either the anaerobic or AGS system and cause strain on both the WWTF's UV disinfection system, by reducing UVT, and effluent TSS limits. photos of the settleability testing and Reduced UVT effluent quality are shown in (Figure 4) and (Figure 5). The pilot study was immediately ceased, and the industry agreed to explore alternative acid sources in the future. In response to these challenges, SSC implemented immediate operational adjustments while exploring the economic feasibility of on-site sulfur management strategies. Both liquid phase and gas phase sulfur management strategies were evaluated, resulting in the decision to pursue installation of a more robust biogas chemical scrubber system. This planned upgrade aims not only to improve biogas quality but also to enhance the economic viability of the biogas produced. Future plans include integrating the upgraded biogas treatment system with a third-party renewable natural gas (RNG) facility, enabling further purification and injection into the natural gas grid. This strategic pivot highlights SSC's commitment to sustainability and innovation in its wastewater management practices. This presentation will delve into the technical specifications of the anaerobic lagoon design, the challenges encountered during the startup phase, and the innovative strategies employed to manage biogas quality effectively. It will also provide insights into the operational adjustments made to mitigate the high H2S levels. Additionally, facility operating data is being used to help develop and calibrate a desktop model of the overall sulfur balance around the facility including gas and liquid phase dynamics with variable loadings and operating conditions. This work will contribute to the broader discourse on effective sustainable biogas and sulfur management practices and innovative approaches in wastewater treatment facilities dealing with similar challenges. This study serves as a case study for other treatment facilities aiming to optimize their biogas management strategies while ensuring compliance with environmental standards and promoting sustainable practices in wastewater treatment.