Furthering the Course of Water: Best Practices for Effluent Treament
Wastewater Treatment Technologies
- Conventional activated sludge process (ASP) This is a suspended growth process used for municipal wastewater treatment. The activated sludge plant involves wastewater aeration tanks with microbial suspension, solid-liquid separation, clarifier, discharge of clarified effluent, wasting of excess biomass, and return of remaining biomass to the aeration tank.
- Extended aeration activated sludge process Extended aeration is the modification of activated sludge process (ASP) and operates in the endogenous phase, the production of cell matter which is producing a minimum of excess sludge to be wasted from the system. The range of F/M‘s to use is that which produces the least BOD5 and suspended solids in the effluent while producing sludge with good settling characteristics.
- Moving media bio-reactor (MMBR) MMBR technology employs thousands of polyethylene biofilm carriers operating in mixed motions, within an aerated wastewater treatment basin. Each individual bio carrier increases productivity through providing protected surface area to support the growth of bacteria within its cells. It is this highdensity population of bacteria that achieves high-rate biodegradation within the system, while also offering process reliability and ease of operation. This technology has the advantage of providing cost-effective treatment with minimal maintenance.
- Sequential batch reactor (SBR) Sequencing batch reactor (SBR) is an activated sludge process. It operates in a true batch mode with aeration and sludge settlement both occurring in the same tank. The major differences between SBR and conventional continuous-flow, activated sludge system, is that the SBR tank carries out the functions of equalization, aeration and sedimentation in a time sequence rather than in the conventional space sequence of continuous-flow systems. In addition, the SBR system can be designed with the ability to treat a wide range of influent volumes whereas the continuous system is based upon a fixed influent flow rate. Thus, there is a degree of flexibility associated with working in a time rather than in a space sequence. The operating principles of a batch activated sludge process, or SBR, are characterized in five discrete periods: Anoxic fill, aerated fill, react, settle, decant.
- Membrane bio-reactor (MBR) A membrane bioreactor or MBR is an activated sludge process that utilizes a physical barrier, the membrane, to filter contaminants from wastewater. Utilizing submerged membranes eliminates the need for secondary clarification and tertiary filtration. By decoupling the activated sludge process from the settling characteristics of suspended solids (MLSS), the footprint of a wastewater treatment process can be halved or more. In addition, a MBR is ideally suited for biological nutrient removal (BNR) applications as coagulated metal salts are easily filtered and captured phosphorous can be collected as waste activated sludge (WAS).
- Up-flow anaerobic bio-reactor (UASB) In the UASB process, the whole waste is passed through the anaerobic reactor in an up flow mode, with a hydraulic retention time (HRT) of only about 8-10 hours at average flow. No prior sedimentation is required. The anaerobic unit does not need to be filled with stones or any other media; the up-flowing sewage itself forms millions of small ‘granules‘ or particles of sludge which are held in suspension and provide a large surface area on which organic matter can attach and undergo biodegradation. A high solid retention time (SRT) of 30-50 or more days occurs within the unit. No mixers or aerators are required. The gas produced can be collected and used if desired. Anaerobic systems function satisfactorily when temperatures inside the reactor are above 18–20°C. Excess sludge is removed from time to time through a separate pipe and sent to a simple sand bed for drying
- Trickling filter/bio-tower Trickling filter is an attached growth process i.e. process in which micro-organisms responsible for treatment are attached to an inert packing material. Packing material used in attached growth processes include rock, gravel, slag, sand, redwood, and a wide range of plastic and other synthetic materials.