Texas Waste Water Treatment Ch#06 Secondary Biological Treatment

Bacteria are the most numerous and important organisms in wastewater treatment, although protozoa, algae, and fungi play important roles. Bacteria break down organic materials into simpler products that can be used as food or be released to the environment. Protozoa usually feed on tiny particles and act like vacuum cleaners to improve effluent quality. Algae may be needed to supply oxygen in stabilization ponds. Fungi can break down waste materials.

Living cells possess two basic cell structures, prokaryotic and eukaryotic (sometimes spelled procaryotic and eucaryotic). This division is based on internal complexity. Prokaryotic cells have a simple structure and lack a distinct nucleus. Their rigid outer cell wall gives them shape; just under this cell wall they have a more fluid cell membrane that carries out metabolic processes. Bacteria and blue-green algae possess a prokaryotic cell structure. Eukaryotic cells, those in protozoa, higher plants, and animals, are highly structured. These cells tend to be larger than the cells of bacteria and have an enclosed nucleus. Eukaryotes also possess organelles, specialized internal cell structures that are enclosed by their own membranes.

Think about what would help or hinder your growth. would you like to be in a desert or tundra with no food? how about drowning in an over chlorinated pool? Bugs will thrive in wastewater treatment systems when they have a balanced food supply and the correct environment. The food supply must contain carbon, hydrogen, oxygen, nitrogen, phosphorous, sulfur, potassium, and trace elements in the proper proportions. A deficiency in nutrients or trace elements will prevent the development of healthy treatment organisms. Major factors that affect the environment include dissolved oxygen, temperature, pH, nutrients, toxic materials, time, sunlight, and competitors and predators. If any of these factors change, the population of bugs in the treatment plant will shift, favoring the groups that adapt best to the new conditions. Operating a wastewater treatment plant is like running a zoo. Microorganisms need to be well fed, in the proper environment, and free of disease and predators. The old or dead bugs must be removed from the system to promote the growth of healthy, young microorganisms.

Bacteria are the primary worker microorganisms (most important) in wastewater treatment plants, usually composing 80% to 90% of the living material.

Bacteria, being very small and indistinct, are difficult to identify. They are often put into categories according to size and shape, oxygen needs, temperature requirements, food needs (metabolism), and the by-products they produce.

Aerobic - relating to, involving, or requiring free oxygen.

Facultative bacteria are microorganisms that can use dissolved oxygen (DO) OR oxygen obtained from food materials such as sulfate or nitrate ions, and some can respire through glycolysis. These bacteria can live under aerobic, anoxic, or anaerobic conditions.

>Food gathering< (biosorption). Food gathering occurs when bugs collect food from wastewater. Food may accumulate in the slime layers on a microorganism, be ingested through an orifice, or absorbed through the cell wall. >Food digestion<. Digestion can be external or internal. It occurs when special organic catalysts (enzymes) break down food into simpler materials that can be consumed by the bugs. >Growth, reproduction, and respiration< (utilization). Utilization occurs when bacteria use the digested food for cell growth, reproduction, and energy. Many complex biochemical reactions must occur for utilization to take place. >By-products< (excretion). By-products of the feeding process include many different excreted materials, such as CO2, H2O, NH3, and polysaccharides.

In general all life needs food, water, and not to be dropped into a vat of boiling acid......

In the treatment plant, the bugs will do their job well and remain healthy as long as food and environmental conditions are carefully controlled. If the food or environmental conditions are not controlled, the bugs may become sick and ineffective, resulting in inadequate treatment of wastewater. In a healthy biological treatment system, the number of bugs will be balanced with the available food supply and the environmental conditions will be stable. As long as the environmental conditions remain stable, populations will be stable.