bioFAS™ Attached Growth Biofilm Systems

BioprocessH2O offers a comprehensive line of high rate attached growth biofilm systems (bioFAS™) designed to provide compact biological treatment processes that are resilient to toxic shocks, easy to operate and require minimal maintenance. BioFAS systems are modular and supplement existing treatment systems for enhanced BOD removal, nitrification and denitrification.

How Attached Growth Biofilm Systems Work

In nature, many bacteria thrive as complex colonies of co-dependent microbes known as biofilms. Found in water, biofilms adhere to a substrate anchoring material such as rock, wood, metal and man-made materials like plastic and linear composites. Aerobic biofilms require water, oxygen and a nutrient food source to maintain cell function. Microbial metabolism causes biodegradation of organic matter and production of metabolic by-products including carbon dioxide (CO2) and deceased micro-organisms. deceased biofilm components slough off the surface of active biofilm by water turbulence, mechanical sloughing or change in environmental conditions including temperature, toxic shocks, load fluctuations, etc.

Biofilm microorganisms adhere to a self-produced matrix of extracellular polymeric substance (EPS) often referred to as zooglea, plaque or "slime" composed of polysaccharides and proteins. The slime becomes a matrix where a great variety of waste digesting microbes are found in stratified aerobic and anoxic zones. Typical organisms include heterotrophic bacteria, nitrifying bacteria nitrosomonas and nitrobactor, stalked ciliates, free swimming ciliates, along with populations of higher order organisms such as rotifers that feed on the dead biomass. Shortly after installation, BioFAS™ biofilm systems attract and fix waste digesting bacteria that degrade organics in a given wastewater stream where select species survive and reproduce through a process of natural selection. BioFAS™ systems can be seeded with bacteria from a municipal wastewater treatment plant using fresh return activated sludge (RAS). In a majority of applications, municipal RAS will contain the micro-organisms required for industrial applications although specialized seeding can be provided to meet requirements of specific wastewater treatment streams.

bioFAS™ Biofilm Treatment Processes

BioFAS™ systems can be configured in modular staged-arrays or treatment trains to provide biological degradation of organics on a single pass. Biofilm systems are typically a fraction of the size (1/4 – 1/3) of conventional activated sludge plants that treat an equivalent organic load.

BOD Reduction – Carbonaceous organics referred to as carbonaceous biochemical oxygen demand (CBOD5) are a food source for heterotrophic bacteria that consume organic carbon. To maintain a healthy diverse biofilm, micro-organisms require oxygen for respiration and macro-nutrients such as ammonia–nitrogen (NH3-N) and phosphorous (P). For every 100 lbs of CBOD consumed, heterotrophic bacteria require 5 lbs of NH3-N and 1 lb of P, the Eckenfelder rule of thumb ratio (100:5:1). For every pound of CBOD consumed, approximately 0.4 – 0.5 lbs of biosolids are generated. Biosolids can be further treated via sludge digestion and dewatering techniques. Dissolved oxygen (DO) requirements for high rate biofilm processes are typically above 3 mg/L to effectively penetrate the stratified zooglea matrix.

Nitrification – Ammonium (NH4-N), a food source for autotrophic nitrifying bacteria nitrosomonas and nitrobactor, is metabolized in a two step biological nitrification process. Nitrosomonas bacteria convert ammonium (NH4) to nitrite (NO2) and Nitrobacter bacteria convert nitrite (NO2) to nitrates (NO3) along with the production of hydrogen (H+). Therefore, alkalinity is required in the wastewater stream to neutralize wastewater during the nitrification process. Under cold water conditions, attached growth nitrifiers outperform activated sludge biological treatment processes without the benefit of a fixed population of biofilm bound nitrifires. DO requirements for a high rate nitrifying biofilm process is typically above >4 mg/L to enhance nitrification rates.

Denitrification – Denitrification is the biolgocial reduction of nitrate to nitric oxide, nitrous oxide and ultimately nitrogen gas in response to the oxidation of an electron donor (such as CBOD5, methanol, etc.). The denitrification process operates anoxically (DO levels of <0.5 mg/L) and is important because approximately ½ of the alkalinity consumed during nitrification is recovered. Many times, the denitrification process is staged ahead of the nitrification process to utilize the CBOD contained in the wastewater as the electron donor. This is known as the Modified-Ludzak Ettinger (MLE) biological nutrient removal process, typically using a 2Q – 4Q nitrate recycle loop to reduce the total nitrogen (TN).