One Size Doesn’t Fit All! Optimizing Biofiltration for Various Source Water Qualities
Biofiltration has rapidly achieved increased nationwide acceptance as a safe and dependable method for enhancing the benefits of conventional filtration through biological treatment. From removal of taste and odor compounds to disinfection byproduct precursors, biofiltration utilizes microbial growth within a filter to enhance water quality beyond particle removal.
For many of the utilities we work with, the primary challenge they face with biofiltration systems is obtaining sufficient microbial growth while minimizing biological fouling, commonly caused by production of extracellular polymeric substances (EPS). Increased production of EPS can lead to hydraulic issues like decreased filter run volumes, underdrain fouling and plant bottlenecks.
To address these issues, HDR has led Water Research Foundation Project 4555 “Optimizing Biofiltration for Various Source Water Quality Conditions” to develop clear and concise guidance for holistically optimizing biofiltration for utility-specific treatment drivers. One of the primary objectives of the study was to synthesize strategies from the past ten years of biofiltration research and determine how source water quality influenced strategy success. The three primary strategies tested were the addition of low doses of upstream oxidants, nutrient augmentation and filter backwashing.
Testing for two years at over ten drinking and recycled water biofiltration systems nationwide demonstrated that one size does not fit all when it comes to biofilter optimization. Like any biological treatment system, every biofilter process will have distinct media characteristics, biological communities and design parameters that impact strategy success. Nevertheless, several strategies presented promising results in both pilot and full-scale systems. For instance, oxidants and nutrients can be implemented relatively easily with minimal (if any!) construction on site.
The application of low doses of unconventional oxidants (chlorine, chloramines and peroxide) to biofilter feed at several utilities yielded reliable and sustained hydraulic performance that did not diminish biological activity or effluent water quality. The goal of the oxidant addition was to dose to demand and ensure that no oxidant residual was measured on the effluent of the filter. At one ozone-biofiltration facility in North Texas, we were able to reduce filter headloss by up to 85% with concentrations as low as 0.5 mg/L of chloramine in pilot-scale granular activated carbon (GAC) biofilters. At another ozone-biofiltration facility in the Mid-Atlantic, filter run times nearly tripled with 1 mg/L of chlorine fed to full-scale anthracite biofilters. In both cases, no significant difference in organics removal, effluent turbidity and disinfection byproduct formation potential was observed.
Additionally, nutrient augmentation was beneficial for select utilities where we sought to identify if a nutrient or substrate limitation was increasing biological fouling in the filters. At one full-scale ozone-biofiltration facility (GAC) in the Mid-Atlantic, 0.1 mg/L of phosphorus supplementation decreased the headloss accumulation rate by up to 30%, lengthening filter run times while meeting treatment objectives.
As already mentioned, both of these optimization strategies were easy to implement. A simple chemical feed system was modified to provide low doses of nutrients or oxidants to test biofilter operation.
Finding sustainable solutions through research projects like WRF 4555 is important to HDR’s Water Institute. We aim to provide the water industry with practical and vetted guidance for improving operation, while avoiding significant cost or operational burdens. We’re excited to share the published WRF 4555 report in early 2018. Inside you’ll find results of pilot and full-scale testing at participating utilities, successful optimization strategies and decision charts to help utilities navigate biofilter optimization.
WRF 4555 Project Principal Investigators (PIs) are Chance Lauderdale (PI), Jennifer Hooper (Co-PI, CDM Smith), and Eric Wert (Co-PI, Southern Nevada Water Authority).