MBR treatment makes water of high quality. All microorganisms, solids, and colloids are filtered out. The produced water can be reused, recycled, or released into the environment. Some users will find the MBR membrane effluent is colored. We will look at the most common reasons for colored MBR effluent and share our experience of dealing with them.
What is the color, turbidity and transparency of water?
Water color is an indicator of substances dissolved within it. Light yellow, brown, or green hues often come from natural components like humic matter. Wastewater color frequently arises from industrial dyes or other unnatural contaminants. Quantitative color measurement sets standards for treated water quality.
Turbidity gauges the level of light passage obstruction from particles suspended in water. It depends on particle attributes like size and shape too. High turbidity raises chemical demand and hinders disinfection performance. Low values suggest lower bacteria and virus levels.
Transparency measures water clarity via the visible depth in special tubes. More particles present lead to worse transparency. It combines color and turbidity influences. For wastewater, suspended solid testing is more common than transparency tests.
What are the false color and actual color for MBR effluent?
With MBR, apparent water color along inspection windows occasionally misleads. Direct outlet sampling then becomes necessary to verify real hue. Yellow, green, brown and more result from incompletely removed content.
False color arises from wall/pipe deposits seen through meters or sight glasses. Cleaning there first is wise to expose true color. Algae growing in storage tanks also misrepresents raw MBR output.
What are the reasons and solutions for the actual color of MBR effluent?
If color remains after direct examinations, typical reasons behind MBR coloration include:
- Insufficient biochemical conversion: Residual ammonia-nitrogen from inadequate biological processing makes effluent appear yellow. Enhancing oxidation of stubborn nitrogen species is key.
- Metal ions: Copper, iron, chromium ions yielding colored compounds pass through membranes. Assessing ion concentration then adding chelating agents to combine ions into less colorful complexes helps.
- Industrial dyes: Small dye molecules used in textile and ink manufacturing permeate membranes. Dye separation via prior coagulation, oxidation or specific adsorbents suit individual cases.
- Chelates: Chelating groups from surfactants or similar chemicals become visible after reactions downstream. Additional oxidation or chromophore destruction works depending on chelate composition.
Broad solutions for actual coloration include:
- Checking biochemical capacity and controlling target indices like ammonia below typical limits through microbial culture adjustments.
- Adding activated carbon filters and adsorbents tailored to adsorb specific colorants based on troubleshooting.
- Applying secondary strong oxidation processes using oxidizers like sodium hypochlorite and ozone.
- Integrating nanofiltration or reverse osmosis membrane separation to filter colorant molecules.
What other methods are available to decolorize MBR effluent?
Beyond prior steps, further techniques to decolorize MBR effluent include:
Adsorption onto recycled or waste-derived media chemically binds color bodies. Activated carbon offers non-specific organic adsorption. Ion exchange suits some metal complex dyes. Cost, water quality influences approach.
Coagulation via inorganic or polymeric flocculant addition aggregates then settles color substances. Widely available steel and aluminum salts work for broad color removal. Cationic and advanced options expand applicability.
Oxidation breaks down colorful compounds or alters conjugation. Chemical (chlorine, ozone, Fenton’s reagent), photolytic, ultrasonic means all destruct chromophores. Balancing costs and complete oxidation governs method selection.
Biodegradation utilizes microbial enzymes to directly cleave colorful functional groups. Culture conditions tuning expands enzyme palette. Economic for biodegradable dyes.
Membrane filtration using tight nanofiltration or reverse osmosis membranes prevents colorant passage. Justifiable for high value reuse applications.
Further details around cost, scalability and discharge guidelines helps match methods to individual cases for optimal MBR post-treatment.
The bottom line
This is our analysis of the MBR membrane effluent color problem. We hope it helps customers who have similar problems. MBR technology is important for protecting the environment. It has a better effluent index and less pollutant emission, so it should be promoted. MBR effluent helps businesses reuse and recycle water, save money, and protect the environment.
