Meeting Stringent Nutrient Limits With Gravity-Fed Biofiltration

Increasingly stringent nutrient discharge requirements are pushing wastewater treatment plants to adopt more advanced tertiary treatment technologies capable of addressing nitrogen, phosphorus, and suspended solids. Gravity-fed biofiltration offers a comparatively simple and energy-efficient approach, using biological processes within a traditional filtration configuration to achieve deeper nutrient removal. Denitrification downflow systems can reduce nitrate nitrogen to low concentrations while producing effluent with low levels of total suspended solids and phosphorus, while biologically activated carbon filters provide additional capabilities for addressing emerging contaminants and total organic carbon. Effective performance depends on proper underdrain design, backwash management, and process control. Uniform distribution of air and water during backwash helps maintain the full filter bed, while appropriately sized media retainers can reduce fouling and eliminate support gravel where retrofit space is limited. Automated controls using dissolved oxygen and nitrate measurements can further optimize backwashing, chemical dosing, and valve sequencing without disrupting biological populations. Combined with low energy requirements, durable components, and adaptable configurations, gravity-fed biofiltration provides wastewater plants with a practical approach to meeting demanding nutrient limits while maintaining operational simplicity and long-term value.