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Recently, I was given the task of designing a small wastewater treatment plant (WWTP) for a smaller enterprise engaged in the production and bottling of non-alcoholic beverages. In this article, I will describe in more detail the technology we have chosen for the case.

For those involved in wastewater treatment who were engaged in this area before, the size of the plant represents 283 people - population equivalents (PE).

For the less interested I will explain the term population equivalent.

It is a very approximate value that imparts water pollution to the number of people / inhabitants who produce the same amount of pollution by their activity and metabolism. Thus, we can objectively assign the WWTP its size.

3 wastewater treatment methods used in small businesses

There are few ways how the company could handle its wastewater.

1.

First of all, if it is possible to connect (under good conditions) to municipal or village sewerage, the management of the company shall certainly take a decision of doing this. It is the least demanding and the most practical way to dispose of the wastewater produced.

The company would pay only to the operator of the municipal wastewater treatment plant for the cost of the sewage disposal which they agreed on in the contract. The role of the enterprise would be to monitor the amount and composition of the water and not to exceed the agreed parameters.

Even this path can even be done more efficiently when wastewaters from production and other wastewater (rain from roofs and hard surfaces) are separated. However, there is a "threat" that an authority might require the enterprise to slightly pretreat other waters that flow directly into the watercourse, as a result of which it would be necessary to design the technology in addition (even if less complicated).

2.

The second alternative works when there is no sewerage near the factory. In this case, the waste water is led into the cesspool, where it is collected and subsequently taken away by  designated vehicles (to the nearest possible WWTP).

This procedure may be assessed as appropriate or inappropriate, taking into account, in particular, the frequency of the removal and the related payments for that service.

3.

The third option is the construction of own wastewater treatment plant which has its positives as well as negatives.

Minuses are certainly the amount of initial investment and regular care needed to keep this technology running properly. As a plus, it is possible to mention its own independence in this respect and no fees for emptying cesspools or discharging wastewater into sewerage system.

Advantages and disadvantages of container wastewater treatment plants

In the context of small treatment plants, as well as the aforementioned production plant producing and filling of non-alcoholic beverages, it is often referred to as so-called container treatment plants.

The entire wastewater treatment process is “pressed“ into a single freight-shipping container. It is a fairly practical solution, because no concrete tanks are required, but everything is still located along the length of twelve meters.

If you need something compact and something that takes as little space as possible, container wastewater treatment is really a good solution.

However, if I should mention some kind of possible “problem“ of this system, it is a deficient depth.

Most of the containers have a height of about 2.6 meters, which is relatively small compared to the depth of the classic tanks at a wastewater treatment plant. Conventional wastewater treatment plants have a tank level of 4 to 4.5 meters, due to the longest possible residence timeof the oxygen in the system.

It is necessary to bring air into the system because of microorganisms that need oxygen to live. And the longer the oxygen in the system, the more it can dissolve itself in the water. If we reduce the water level in the tank, less oxygen will dissolve in the system. 
Therefore, it is necessary to supply larger volumes of air.

As we increase its amount and basically use it inefficiently, we lose money in the form of kWh consumed by a blower that ensures the air supply.

For small plants, a very uneven flow can be a drawback, from zero - when the factory works only for one shift and the rest of the time only idles, up to maximum inflows, for example, when washing and cleaning of the production line.

Therefore, it is advisable to propose an equalization tank prior to such technology that will mitigate the irregularity in the inflow and also the irregularity in the composition (pH, temperature, concentration of various substances, etc.).

Conclusion

In any case, however, I can not unambiguously condemn the container treatment plants for success or failure. 
Like any technology, this one has its advantages and disadvantages as well as the situation and context of the factory, where just such a type of wastewater treatment plant literally calls for application.

If you don´t know what solution would be ideal for your business, we'd  be happy to advise you.

Author: Ing. Matúš Palguta, chemical technologist