Innovative technologies are helping the Metropolitan Sewer District of Greater Cincinnati (MSD) improve water quality in local streams and rivers while keeping costs in check.
The technologies, which range from satellite imagery to algae from the South pole and real-time controls to DNA genetic markers, are highlighted below.
Reducing sewer overflows and costs through real-time controls
Like a number of utilities across the nation, MSD is faced with a federal mandate to address water quality impairments caused by combined sewer overflows (CSOs), a mixture of raw sewage and stormwater. During a typical year, about 11 billion gallons discharge from more than 200 combined sewer overflow (CSO) outfalls along local rivers and streams. The utility is under a $3.1 billion unfunded Consent Decree to reduce the overflows, with hundreds of sewer and stormwater projects slated for construction. With costs passed along to customers through ever-increasing sewer rates, MSD is seeking new and less expensive ways to address wet weather issues.
In early 2015, MSD deployed its Wet Weather SCADA system covering Mill Creek, its largest watershed. This transformational technology is designed to use available storage capacity in existing sewer infrastructure (e.g., interceptor sewers, storage tanks or high-rate treatment units) to avoid overflows, in lieu of building expensive new infrastructure.
The system uses sensors to provide real-time monitoring of wastewater flows in the sewer system over large geographic areas, a sophisticated SCADA-based computer system, and the physical control of flows. Within the first several weeks of operation, the technology was used to store flows at a high-rate treatment facility, avoiding 1.4 million gallons in overflows at a location nearly 11 miles away. The Wet Weather SCADA technology is being advanced in other MSD watersheds and is anticipated to save tens of millions of dollars in capital investments in wet weather projects.
Detection of pollutants and pollutant loading
Many different pollutants and pollution sources can contribute to a decline in water quality.
MSD is responsible for reducing sewer overflows, but it’s hard to improve water quality with continuing discharges from industries, leaking septic tanks and runoff from dog parks, residential areas and farmland.
To address this challenge, MSD is exploring three technologies to help detect and measure pollutants and their sources and use that information to prioritize capital projects that achieve the biggest bang for the buck. Understanding the true cause of water quality impairment is a huge benefit when it comes to making decisions addressing major pollution issues.
- DNA Source Tracking: MSD partnered with the U.S. EPA and University of Cincinnati to develop an analytical laboratory method that uses DNA and RNA (genetic markers) to detect where pollutants in local streams and rivers are coming from and their quantities. The genetic markers can tell you whether the pollutant is animal fecal matter or from a human and can also identify pollutant loadings such as sewer overflows vs. leaking septic systems.
MSD is using this information to support decision-making for capital projects related to sewer overflows or stormwater management. The method also helps MSD communicate and collaborate with other local agencies, such as the health department, park district or environmental services to reduce water quality impacts from other sources.
- Remote Sensing: MSD is pilot testing a new technology that uses satellite images of local streams and rivers – combined with a proprietary algorithm – to detect pollutant loadings and hot spots on a watershed scale. The technology was developed by Blue Water Satellite, Inc. with the assistance of Black & Veatch, a national design engineering firm. One pilot study focused on total suspended solids, phosphorus, phycocyanin, and chlorophyll-a in the Ohio River during normal river conditions. A second pilot study looked at hot spots in communities on septic systems.
- Decision-Making Tool: MSD is using a decision-making tool called the Integrated Prioritization System (IPS) that analyzes water quality monitoring data and presents it in a comprehensive Excel-based database format. Developed by the Midwest Biodiversity Institute, the tool allows users to query, view, map and export data summarizing the conditions of local streams and rivers. The IPS accesses recent water quality monitoring data for the Little Miami, Mill Creek, Great Miami and Ohio River basins, as well as historical monitoring data prior to 2011.
New Treatment Technologies
As a wastewater utility, MSD is charged with treating sewage and discharging clean effluent that meets water quality standards and complies with environmental permits.
- Future of Disinfection: Disinfection of treated effluent prior to discharging it into a local stream or river is an essential part of the wastewater treatment process. Although most solids, organic matter, and metals are removed from wastewater during the treatment process, the effluent still contains bacteria, viruses and other disease-causing organisms. Disinfection is the only way to destroy these pathogens to maintain water quality and prevent disease.
MSD’s plants currently use sodium hypochlorite (liquid chlorine) or ultraviolet (UV)-based systems. Both methods are highly effective, but are either expensive (UV) or create byproducts (sodium hypochlorite), many of them toxic.
To address these challenges, MSD is currently evaluating paracetic acid as a potential new disinfectant. Testing in the lab showed that paracetic acid met the following criteria:
- Powerful enough to neutralize a wide spectrum of bacteria, viruses and other microorganisms
- Effective with a short contact time
- Does not produce any toxic byproducts
- Does not require neutralization after disinfection treatment
- Not affected by the type of contaminants and level of organic matter in the wastewater
- Safe to use and store
MSD is now preparing for a pilot study to validate the lab data. MSD’s ultimate goal is to improve the environment, conserve energy, and reduce the cost of wastewater treatment at MSD plants by switching to paracetic acid.
- Using Algae to Fight Algae: Wastewater is loaded with organic matter and nutrients like ammonia and phosphorus. During warm weather, nutrient-loving microorganisms or “bugs” in the secondary aeration tanks do a great job of “eating” the excess nutrients. But during colder weather, the bacteria can become dormant, causing increased levels of nutrients in the effluent discharged to local streams and rivers, which can potentially lead to permit violations or algal blooms.
To address this challenge, MSD is developing an all-weather, algae-based technology to remove and recover nutrients from wastewater. A native Ohio algae and an algae from the Antarctic (South pole) have been tested in the laboratory and show promising results. MSD is now focusing on pilot studies of both strains of algae, with the goal of blending the two types of algae to create a nutrient removal system that works in all temperatures.
Besides removing nutrients from effluent, this technology also has the potential to reduce the cost of sludge incineration. Excess algae, which has been dewatered, has a very high fuel burn rate and can be mixed with sludge prior to incineration to reduce the amount of natural gas needed to burn the sludge.
