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STP Performance in Winter: What We Changed After BOD Removal Dropped Below Compliance Limits
Overview
This blog looks at a winter STP problem from the operator's point of view: BOD removal started falling even though the equipment was running normally. It explains how low temperatures can slow bacteria in the aeration tank and affect treated-water results. It also covers the checks operators should make before changing the plant settings. The blog then explains where low-temperature bacteria, such as Amalgam Biotech's Cold Region Bacteria STP, can fit into winter sewage treatment.
The first sign was not a pump failure or a blower problem. It was the BOD report.
The treated-water BOD had started rising as the weather became colder. The plant was running as usual, but the results were no longer where they needed to be. We checked the inlet wastewater and found no major rise in the organic load. The next place to look was the aeration tank.
That was when the effect of winter became clear.
Table of Contents
The BOD Drop Started With the Cold Water
An STP depends on bacteria to break down organic matter in sewage. These bacteria are affected by water temperature.
When the water gets colder, they can work more slowly. This can reduce BOD removal in STP systems.
The change may not happen overnight. In many plants, the treated-water BOD starts moving up slowly over several days or weeks.
This is one reason STP performance in winter needs closer attention.
We Checked the MLSS Before Making Changes
The first thing we checked was MLSS.
MLSS contains the microorganisms that do much of the work in the aeration tank. When temperatures fall, MLSS activity can drop.
We checked the MLSS level, sludge settling, dissolved oxygen, and BOD results together. Looking at only one number would not have told us much.
This also helped answer a common question: why is MLSS less active in winter?
The answer is mainly linked to temperature. Cold water can slow the activity of the microorganisms in activated sludge.
We Did Not Simply Increase the MLSS
It can be tempting to add more sludge when BOD removal starts falling.
But more MLSS does not automatically mean better treatment.
The existing sludge may already be present in sufficient quantity. The issue may be that the bacteria are not working at the same rate because of the lower temperature.
So, we checked the other operating conditions first.
Dissolved oxygen was checked. Aeration equipment was inspected. Sludge settling was watched more closely. Inlet and outlet BOD readings were compared.
This gave us a clearer picture of what was happening inside the plant.
What We Changed During Winter
Once low temperatures became a clear factor, we looked at the bacteria being used in the plant.
Normal wastewater bacteria can become less active when temperatures fall. This can affect biological treatment efficiency and slow the breakdown of organic matter.
We considered bacteria selected for colder conditions.
Amalgam Biotech's Cold Region Bacteria STP is made for wastewater treatment where low temperatures can affect bacterial activity. It contains selected microorganisms intended for use in cold conditions.
It can be used as part of a winter treatment plan when microbial activity has slowed.
It does not replace proper aeration, MLSS control, sludge management, or regular BOD testing.
How Cold Weather Affects Sewage Treatment Plants
Cold water can slow the bacteria that consume organic matter; when their activity drops, the treatment of BOD can also slow.
This is especially important in plants where wastewater temperature falls sharply during winter.
The result may be higher outlet BOD, changes in sludge settling, and slower treatment.
That is why cold weather wastewater treatment needs regular checks when temperatures start to fall.
How to Improve BOD Removal During Winter
There is no single setting that will fix every winter STP problem.
If you want to know how to improve BOD removal during winter, start with the test results.
Check:
Wastewater temperature
Inlet and outlet BOD
MLSS
Dissolved oxygen
Sludge settling
Sludge age
Aeration equipment
If these checks show that cold water has reduced bacterial activity, low-temperature bacteria may be worth considering.
Cold Region Bacteria STP from Amalgam Biotech is one such product made for colder wastewater conditions.
Winter Operation Tips for STPs
Good winter STP operation starts with regular observation.
Check wastewater temperature instead of assuming it has stayed the same. Keep an eye on BOD results. Watch MLSS and sludge settling. Check that blowers and diffusers are working properly.
Also avoid making several changes at the same time. If the BOD result improves, you need to know which change made the difference.
These simple winter operation tips for STPs can make troubleshooting much easier.
What We Learned From the BOD Drop
The main lesson was that a winter BOD problem does not always mean that the equipment has failed.
The plant was running. The problem was happening inside the biology.
Lower temperatures had reduced microbial activity in cold weather, and the change showed up in the BOD results.
For STPs facing this problem, checking temperature, MLSS, aeration, and BOD together is a better starting point than making random changes.
Where cold temperatures are affecting the bacteria, Cold Region Bacteria STP from Amalgam Biotech is an option to consider for winter wastewater treatment.
Keep Your STP Performing Through Winter
Cold temperatures can slow microbial activity and affect BOD removal even when your equipment is operating normally. Support winter biological treatment with a low-temperature bacterial solution suited to STP conditions.
Frequently Asked Questions
1. Why does STP performance decrease in winter?
STP performance decreases in winter because low wastewater temperatures can slow the bacteria that break down organic matter. This can reduce BOD removal and affect activated sludge performance.
2. How does cold weather affect sewage treatment plants?
Cold weather can reduce microbial activity, which may slow the breakdown of organic matter. This can lead to lower BOD removal and changes in sludge settling.
3. How can we improve BOD removal during winter?
To improve BOD removal during winter, check wastewater temperature, MLSS, dissolved oxygen, sludge settling, and aeration. If low temperature is reducing bacterial activity, low-temperature bacteria may be used according to the product instructions.
4. Why is MLSS less active in winter?
MLSS is less active in winter because the microorganisms in activated sludge can become slower when wastewater temperature falls. This can reduce their ability to break down organic matter at the same rate.
5. What are the best winter operation tips for STPs?
Useful winter operation tips for STPs include checking wastewater temperature, testing inlet and outlet BOD, monitoring MLSS, checking dissolved oxygen, and inspecting aeration equipment. Plants can also consider bacteria made for low-temperature wastewater when microbial activity falls.
