Treatment

A thoughtful wastewater operator

Wastewater Treatment

Both municipal and industrial wastewater treatment topics will be covered and distinctions between the two will often be made. And there is good reason for this. A distinction is made between municipal and industrial wastewater treatment because, in a municipal wastewater treatment plant, with NO industrial component, the operators will not, generally, be dealing with inhibitory or toxic contributions to their plant. That is not to say that the wastewater they treat is completely predictable. They will be dealing with changes in the wastewater flow rate, getting more flow in the morning as people wake up and begin to prepare for their day cooking, washing, etc. The flow will then taper off as people leave their homes and go off to work. The flow will begin to increase again in the late afternoon to early evening as people return home and once again go about their routines of cooking, cleaning, washing, etc. This is called the diurnal flow pattern that characterizes so many municipal wastewater treatment systems. And the municipal wastewater operator will be dealing with seasonal changes in the wastewater temperature which, as it begins to drop, will slow the rate of nitrification for those plants that do indeed have to nitrify.

At the other end of the spectrum, an industrial wastewater treatment system, such as those in the chemical and petrochemical industries for example, with little to no sanitary wastewater contribution, will find themselves grappling with many potentially refractory and/or inhibitory compounds in the wastewater combined with a very stressful wastewater environment in terms of such parameters as wastewater pH, oil concentration, organics or COD concentration, and temperature, to name a few.

In addition, one of the most significant differences I see between municipal wastewater treatment systems and industrial systems is that the industrial plants are “undersized” for the flow and/or the organic load they are forced to treat. There are many reasons for this. In some cases, production has expanded with little to no allocation of funds to also expand the wastewater system. In other cases, the very nature of the production process has changed based on a major change in the raw materials being used. In the case of refineries this can readily be seen where “sweet” crude oil is being supplemented at ever greater rates with “sour,” synthetic crudes. We will discuss this in more detail later. The point is, though municipal and industrial wastewater systems share many things in common in terms of unit processes, the nature of the waste streams being treated, and the impact of those waste streams on the biological reactor, the activated sludge process, are dramatically different.

There are three major categories under wastewater: 1) activated sludge, oxygen consumption, and 2) polymer.

Activated sludge is the heart of a biological treatment system so the reason for this category is obvious. Intimately associated with activated sludge is oxygen supply and oxygen demand in the bioreactor. A common problem in the industrial area of wastewater treatment is an insufficient oxygen supply to the biological reactor. Three methods for estimating oxygen consumption are provided.

In the municipal sector, polymer is used primarily for sludge dewatering applications. Seldom is polymer used to help activated sludge solids settle in the secondary clarifiers. In the industrial sector, polymer is often needed to improve solids settling in the clarifier in addition to its use as a dewatering aid. The more stressful biological environment in an industrial wastewater system has a very distinct, very negative impact on settling. The use of polymer becomes very important, and very costly if used incorrectly. So a detailed discussion regarding polymer use, polymer selection, and jar testing is provided.


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