Optimization of small sewage treatment plants

We hope that you have come well into the new year and would like to start it with the subject on which our esteemed colleague and product manager Torsten Zelmer gave his presentation "Improvement and optimization of the treatment performance of small wastewater treatment plants" at a BDZ conference in Wittlich.

"Does a wastewater treatment plant with a COD of 180 mg/l in the sample really function poorly?"

How do we come up with such a silly question? The answer seems so simple after all:

"Sure, you can see it!"

If the limit is 150 or even 90, then 180 is a massive exceedance point.

Now most of you will have just finished your annual maintenance cycles or are about to have spring maintenance. And of course, one or the other deviation has been detected in the laboratory analysis. In isolated cases, massive upward breakouts have even occurred.

The first (and understandably simple) impulse is to blame inadequate plant technology for non-compliance with the limit values. But in some cases, this is simply too short-sighted.

According to Mr. Zelmer, there are four relevant assessment criteria for the treatment performance of a CCW plant:

Wastewater composition
Tank technology / hydraulics
Process / control technology
Technical equipment
It is so easy to describe the plant technology as deficient. Best of all, if you have not installed the plant yourself. But as a rule, technical wastewater treatment plants in Germany have received their approval on a test field of an independent testing institute. This means, first of all, that they work.

Of course, one should clarify in advance whether the process fits the circumstances.

Wastewater composition:

In developing our small wastewater treatment plants, we assume an idealized wastewater composition. There is no such thing as standardized wastewater.

If we assume, for example, the average value of 90% expected purification performance throughout Europe, it is worthwhile to take a look at the concentration in the primary clarification. Heavy loads, e.g. grease in high concentration, may well be reflected in a COD of 2,000 mg/l in the influent.

Tank technology/hydraulics:

When it comes to tanks, the material can make a big difference. For example, plastic tanks can be a poor choice in conjunction with very soft water, among other things, because unlike concrete tanks, they cannot release "lime reserves" into the wastewater to positively affect the acid buffer capacity of the wastewater.

In addition, the components tightness of the tank, mechanical cleaning performance, the structural equipment and the sludge storage capacity of the primary clarification play a decisive role for the further treatment.

Process/control technology

It should certainly be clear to everyone that oxygen input is one of the main issues in wastewater treatment. But also the relation of nitrification to denitrification and the relation of pH-value and acid capacity of the wastewater should be considered in case of insufficient wastewater treatment - as already mentioned above - as well as the quality of the biomass in the reactor.

Technical equipment

In order to maintain the treatment process effectively and permanently, the materials and aggregates used must of course be adapted to the system. Characteristic curves and properties of all components used must be selected in such a way that these plants have sufficient reserve to maintain a continuous process even in the event of fluctuations or deviations in standards. The following often applies: less (technical input) is more!

Finally, of course, the sampling is decisive. A sample can only be as good as the person taking it.

Conclusion of this article:

Only by assessing all relevant criteria and their impact can meaningful optimization be achieved.