Over the past few months, I have been contacted by operators seeing an unusual buildup of tiny snail shells in the clarifier weirs and chlorine contact/UV disinfection chambers. For the snails to develop - the facilities are running extremely well with excellent water quality entering the secondary clarifiers.
With such clean water with low color and turbidity, algae can thrive on the walls and weirs in the clarifier and UV chambers. Once you have algae, the pouch snails have a food source and begin to multiply. How can the snails be brought under control?
Most effective way is to remove the snail food source or algae from the clarifier weir & walls. Options to remove the algae include:
Adjusting the pH up in wastewater can be tricky. Ofter people want to use sodium hydroxide or caustic as it works very fast to increase pH and is low cost. The biggest problems with caustic are:
When handling gasoline, diesel, oil, or any other fuel, spills onto surrounding concrete and soils occasionally occur. In such spills, contamination is usually within a few inches of the surface and is an ideal candidate for immediate, in-situ bioremediation. Why pursue in-situ bioremedation?
Environmental Science & Technology, an ACS journal, had an interesting article on how upgrading a municipal wastewater treatment plant to full nitrification activated sludge has impacted the fish population in a downstream river. Before upgrading the wastewater plant to remove nitrogen/ammonia, the rivers population of rainbow darter (etheostoma caeruleum) had intersexed males between 70 - 100% in the previous 5 years. After the upgrade - the WWTP effluent had lower nutrient discharges but also reduced pharmaceuticals and other estrogen mimics. The rainbow darter population quickly reverted to less than 10% intersexed males - an indicator of improved water quality.
While the facility did not set out to treat micropollutants - residual pharmaceuticals and other recalcitrant organic chemicals - improving other parts of treatment with longer exposure to desirable microbial metabolism does improve effluent quality. My current research is on how much we can improve existing biological treatment units with respect to micropollutant removal. If you could remove a majority of the complex compounds in the biological unit, there will be less need for more expensive activated carbon or oxidation technologies to polish off the remaining micropollutants.
Here information on the article and a link to the abstract:
“Reduction of Intersex in a Wild Fish Population in Response to Major Municipal Wastewater Treatment Plant Upgrades”
Keegan A. Hicks*† , Meghan L. M. Fuzzen†, Emily K. McCann†, Maricor J. Arlos†, Leslie M. Bragg†, Sonya Kleywegt‡, Gerald R. Tetreault§, Mark E. McMaster§, and Mark R. Servos†. Environ. Sci. Technol., Article ASAP DOI: 10.1021/acs.est.6b05370 Publication Date (Web): December 27, 2016
- Many smaller wastewater systems do not have to meet stringent nitrate or phosphate permits at their discharge. Instead, they mainly treat for BOD/COD, pathogen, and ammonia removal. Often this system is based on extended aeration activated sludge concepts designed to combine aerobic treatment and some sludge stabilization/digestion in the main wastewater treatment unit. Often the wasted sludge is treated in a small aerobic digester on-site.
With budgetary costs being a concern, I want to point out a potential way to solve some of the secondary floating sludge problems while also lowering utility costs associated with aeration.
When removing ammonia in aerobic activated sludge treatment systems, the final nitrogen form is nitrate (NO3). Many wastewater bacteria can utilize nitrate to remove BOD/COD when dissolved oxygen falls below measurable levels - this is also ORP or Redox below 0 mV.
Often we find this BOD (food) + nitrate with no dissolved oxygen - if we allow the secondary clarifier blanket to build (solids anoxic for over 2hours) with relatively warm temperatures. This results in floating sludge carried by very fine nitrogen gas bubbles. While more of a nuisance than critical problem, in summer conditions this may cause effluent TSS permit issues.
Cycling back the nitrate rich water with the return sludge line and mix with BOD rich influent water, allows existing biomass to degrade BOD while removing nitrate even without a true denitrification reactor. As most conventional municipal ASU facilities are plug flow in design, you can denitrify by reducing aeration in the first portion of the basin. This does not mean fully cut off aeration - as you need enough for mixing if there is not other mechanical mixing present. The reduced dissolved oxygen will drive flocculated bacteria to use nitrate as an alternative electron acceptor while treating soluble influent BOD. The result is a lower demand for added oxygen/aeration while concurrently removing nitrate/nitrite responsible for floating secondary clarifier solids.
Additionally floc forming bacteria are preferentially selected by influent anoxic zones over most filamentous (bulking) microbes. Therefore, the use of denitrification at the head of the aeration basin may also contribute to better SVI in the secondary clarifiers.
I often get requests for Ammonia Oxidizing Bacteria (AOB) and Nitrite Oxidizing Bacteria (NOB) for use in aquaculture ponds. Most often, the delicate AOB and NOB cutures are not what the aquaculture facility needs as the problem isnot readily solved by adding in such specialized cultures.
First, we need to look at aquaculture pond ecology to understand the role of AOB/NOB bacteria. In the pond, ammonia evolves from degradation of animal wastes and excess feed (especially high protein feeds). The ammonia is partially consumed by heterotrophic bacterial growth as they use ammonia as a nitrogen source to build new cells, proteins, enzymes etc. Additionally, nitrite and nitrate are used as an electron acceptor (oxygen sources) in anoxic zones in the bottom sludge. This is why ponds with deep sludge layers often have small nitrogen gas bubbles appearing in quiescent zones.
Most of the remaining nitrogen is used by beneficial eukaryotic algae. These algae uptake nitrogen and produce biomass that is consumed by the animals. Additionally, during daylight hours the algae help to oxygenate the water via photosynthesis. Algae can become a problem when prokarytoic cyanobacteria take over the photosynthetic organism niche. These organisms produce compounds that can cause off-flavor, are often associated with pH swings, and are often not as efficient at reducing ammonia/nitrite concentrations.
A healthy pond has a small background population of AOB/NOB bacteria just like the surrounding soils. This population is small because the amount of substrate (food) for the AOB/NOB populations is actually low. A wastewater tretament plant with 30 - 40 mg/L ammonia does not support an extensive population of AOB/NOB - so imaging an aquaculture pond with only 3 - 4 mg/L ammonia. Adding a concentrate of AOB/NOB may cure the problem quickly, but the population of AOB/NOB will rapidly drop to natural background levels.
An addiitional problem with AOB/NOB concentrates is their need to be refrigerated and their short shelf-life (3 - 6 months maximum). Without refrigeration, the AOB/NOB concentrate drops in activity to what you see in natural waters. So what can be done to prevent ammonia and nitrite from impacting the fish or shrimp?
My key answer is that microbial additives in aquaculture need to be started before problems arise. Using waste degrading microbes early will help with pollution related stress, disease, and keep the desired ecological blance between animal stock, waste degrading microbes and algae.
Usually present in low concentrations, Nocardia sp. of microbes can cause foaming problems when conditions promote a bloom and associated hydrophobic biological polymers. Nocardia foam is dark brown, stable, and viscous. Under the microscope, the foam contains substantial amounts of biomass in the matrix. Easily identifed by branching and gram positive stain, Nocardia organisms and foam are readily identifed by on-site operators.
Nocardia over-growth is encouraged by the following:
Erik Rumbaugh has been involved in biological waste treatment for over 20 years. He has worked with industrial and municipal wastewater facilities to ensure optimal performance of their treatment systems. He is a founder of Aster Bio (www.asterbio.com) specializing in biological waste treatment.
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