Inefficiencies in Municipal Wastewater Treatment Plants
Many Wastewater Treatment Plants (WWTP) were built at a time when budgets were not so tight and engineers erred on the side of caution to ensure that the plant met the design criteria. Many WWTP operators only have experience at one WWTP where they learned the trade from the previous operator. Those operators may have learned how to run the plant from the engineer who designed the facility and never changed their operations approach to adapt with the times.
What some call the municipal approach, “if a little is good, more must be better”, is often seen at smaller plants. This can lead to many unseen expenses. There are three areas that can provide big savings: energy usage, chemical addition, and sludge generation and disposal
The largest typical waste of energy in a WWTP is over aerating. The specific amount of air needed for a well running plant varies with the type of treatment process and the control capabilities. Activated sludge plants require a specific volume of air for BOD removal and nitrification. Online dissolved oxygen monitoring equipment can lead to a very efficient system if the associated controls are installed at the blowers. If these controls are not available, the operator has to select blower settings that allow for the plant to operate within the desired dissolved oxygen levels for the longest period of time possible. Dissolved oxygen will vary with changes of temperatures meaning that spring and fall are the most difficult seasons to maintain consistent dissolved oxygen levels.
Chemical addition is an area where waste often occurs. The ideal way to determine appropriate dosage is to perform jar tests. You add various dosages of chemicals to equal volumes of sample to determine which dosage provides the best flocculation and settlings to achieve desired treatment results. Overdosing of chemicals can lead to excess floc formation, sludge generation, and inhibit settling. If a facility doesn’t have the ability to perform jar tests, a chemical representative will typically give you a starting dosage and adjustments can be made by using visual analysis and laboratory data.
Sludge generation can be impacted by multiple operations approaches. Overdosing chemicals can lead to excess sludge generation and disposal requirements. Excess wasting can also generate increased levels of sludge. Each biological process requires sufficient biomass to treat the level of contaminants in the waste stream. Proper monitoring and control of the biomass will lead to optimum levels of sludge generation.
Multiple options are available to achieve cost effective disposal of the sludge generated from the treatment process. The majority of plants contract to have sludge hauled off-site. The volume of sludge to be hauled can be managed through various thickening processes selected by considering cost of the thickening equipment vs. actual hauling costs. Disposal options range from the least expensive, agricultural land application, to mine reclamation and landfill disposal, which is typically the most expensive disposal method. Some facilities have reed beds which have no annual disposal costs, but require a large capital outlay when they need to be cleaned out. A few facilities have incinerators which are labor intensive and come with high operating and maintenance costs.
The bottom line is that small changes in the treatment process can have a significant impact on the cost of operations. SSM can provide assistance to optimize operating costs for municipal facilities searching for budget dollars.
FOR MORE INFORMATION: Carl Kline, LO