Identifying and Managing Annual I&I Issues
Where does the sand in wastewater treatment plants come from? The answer is the collection system. Determining whether or not there is an issue can be the real challenge. Spring is just around the corner, and with it, the time of year when most of the country’s rainfall usually occurs. Throughout the wet season, an increase in flow into a WWTP can be due to inflow and not an increase in domestic wastewater collected, and potentially a reliable indicator that treatment capacity has been compromised and may need to be restored.
Over time, sand seeps into pipes and lift stations and is eventually transported to WWTP infrastructure. Sand, unlike other debris such as rag material, FOGs, and grit, is an unintended consequence of increased inflow into collection systems. During heavy rainfall, wastewater collection pipes receive an inflow of rainwater which seeps into the pipes transporting sand. Seepage bringing sand usually occurs without notice until the associated problems have become acute and require immediate attention.
I&I issues tend to be out of sight, out of mind. The consequences of I&I tend to go undetected due to the fact that pipes are buried underground and since the water in tanks at the WWTP is not see-through, accumulated sand at the bottom of tanks remains unseen and unnoticed.
Eventually, the increase of sand into wastewater treatment infrastructure can reduce treatment volume and increase energy use. Consider the value of: First, restoring capacity versus replacing capacity when the sand is removed, capacity is restored in the structure at the WWTP. Second, the capital cost to repair or replace pipe segments that may have high inflows. Often, the first solution to solve I&I issues is to repair or replace the pipes; however, the cost-benefit of removing sand from the WWTP that is seeping into pipes may be more cost-effective than fixing the pipes. For example, if the annual cost of maintenance is less than the cost of borrowing the capital to do the repair or replacement project, then removing sand at the WWTP may make more sense, especially given it is an immediate remedy of the unintended consequence of reduced capacity. Finally, the benefit of reducing the amount of energy required to run blowers by removing sand can be significant.
When average daily wet season flows increase significantly compared to the dry season, then sand transported into the collection and treatment systems may be accumulating until it gets your attention. Don’t be taken by surprise; our dependable and knowledgeable team can assist in building your preventative maintenance plan to help. Call (844) 765-7866 to customize a plan for your facility.