Dear Team
What should be minimum DO need for the biological sewage treatment process.
I am getting nil or getting negative value in DO meter. What might be the reason for the same.
Several types of biological processes can be used to treat wastewater, including activated sludge process, constructed wetlands, and various types of filtration. Generally speaking, these methods can be divided into aerobic and anaerobic processes.Sewage treatment is the process of removing contaminants from wastewater, primarily from household sewage. It includes physical, chemical, and biological processes to remove these contaminants and produce environmentally safe treated wastewater (or treated effluent)
Biological treatments, which use organisms to break down organic substances in wastewater, are widely used around the world. Unlike other waste water treatment which use only mechanical or chemical processes, biological treatments include the use of bacteria, nematodes, or other small organisms.Biological wastewater treatment is often used as a secondary treatment process, which means it is used to remove material remaining after primary treatment (the stage in which sediments or substances such as oil are removed from the wastewater).
1. Aerobic Wastewater Treatment
Aerobic wastewater treatment processes include treatments such as activated sludge, oxidation ditches, trickling filter, lagoon-based treatments, and aerobic digestion. Equipment may include diffused aeration systems or mechanical surface aerators, such as RWL Water’s Tornado aspirating aerators, in order to maximize oxygen transfer and minimize odors as the wastewater is treated.Anaerobic Wastewater Treatment
2. Anaerobic treatment is a process that uses bacteria to break down organic material in an oxygen-free environment. Lagoons and septic tanks are example implementations of these types of anaerobic treatment methods.
Negative DO values indicate that the condition in the system is anaerobic. Therefore any biological treatment in that case can be through the action of anaerobic bacteria. Depending on the biological treatment employed, the minimum DO should support the activity of the bacteria/micro-organism concerned.
Most likely is that you are overloaded/under-aerating,
It may be a poorly-calibrated DO meter.
Location in a stagnant zone may also result in low/negative DO.
What kind of DO meter are you using?
Low/negative DO readings with chemical head meters may indicate a fouled membrane. A faulty membrane usually results in an over-reading rather than under-reading.
Low/negative readings may also indicate that the chemical reservoir is depleted and it is time to buy a new head.
Dear Srinivasan,
You will have to tell us the objectives of your treatment. What do you seek to achieve e.g. Removal of organic carbon, removal of Nutrients (N&P) or all of them?
based on your objectives we can advise you. For example, to remove COD you'll have to characterize your wastewater first and specify how much biodegradable COD you have and that will guide how much oxgen you need to supply to the system to oxidise the oxidisable organics through mediation by microorganisms e.g. earobes like heterotrophic bacteria.
based on your objectives you may eeven not need the DO to be present e.g. Anaerobic treatment which is mediated by anaerobes.
You may want to check the following discussion for its possible interest for your query: https://www.researchgate.net/post/What_is_the_proper_way_to_perform_DO_probe_calibration
To answer your first question: the minimum DO concentraton for aerobic treatment of wasatewater should be 1.5 mg.L-1 to 2.0 mg.L-1.
The second question: I fully agree with Jeremy Dudley ´s answers.
Best regards
Vit
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