Contribution of Healthy Microbial Community and Impacts

Immediately after commencement of first ever sewage treatment plant, it was evident that wastewater treatment facilities would serve as a crucial barrier between anthropogenic activities and environment. As stated in one of the UN reports, “roughly 83 million people being added to the world’s population every year” (world-population-prospects-2017), the proportional increase in commodity demand is also expected to be observed. That in-turn will lead to generation of much higher amount of effluent than being treated all over the globe. Advancement of technologies and increase in span of product reach also implies that, not just industries, but effluent treatment community will have to deal with transitions and fluctuations on daily bases. Are we really ready for that? The answer is, to meet new permissible limits, pace of growth and environmental protection policies it is required to come up with innovative, efficient, market viable solutions from research end. The solution lies in microbial community composition present in the sewage or industrial wastewater treatment plant.

Apart from meeting these legislative requirements, plant operation experts face a lot of issues like; excess foam formation, low sludge volume index, low MLSS (in case of industrial effluent treatment plants), slurry formation, unhealthy floc formation and foul smell at various days of the year. If we look into matter of each specific case, microbial community composition holds the key for resolving everyday troubles too.

In this article I would like to brief readers about following points

• What are microbial community and its structure?

• How its composition affects wastewater treatment efficiency?

• General measures affecting composition

• How do we take advantage of useful microbes?

. Wastewater treatment plants are one of the finest examples of microbes (aerobes and anaerobes) being put to work for benefit of human race. Amongst most popular technologies, anaerobic treatment options do serve purpose of removal of toxic material, but fails to meet lower HRT desired in most cases. This limitation can be overcome by aerobic treatment technologies easily due to rapid growth rate of aerobic microbes. However, this condition can only be achieved if the microbial community composition is the best suitable for the wastewater type being treated. It is required to understand that while dealing with aerobic microbial treatment schemes, a single change form optimum parameter will generate direct impact on treatment efficiency. During the biological treatment, group of microorganisms which act on organic waste for its oxidation and the community developed during the processes of CETP holds the key for the efficient functioning of the plant (Forster et al. 2003). Let us try to understand interplay of wastewater and microbes at large using basic microbiological understanding.

The term “Microbial community” refers to assemblage of variety of species of microorganisms living together in the same niche/space/ecosystem/matrices. As illustrated in figure 1, a single organism of single type is normally referred as presence of species A or B. Organism of the same species in bulk is referred as population of species A or B. In a particular habitat, assemblage of multiple numbers of species in billions of numbers is thus referred as community in this article.

. When microbial community present in wastewater comprises single or only two types of microbial population, they are referred to as less diverse population. The population present are called “Dominant population” of the community. Such features, types of population and their numbers are called as structural features of microbial community. Wastewater treatment plants with such dominant species will not be able to utilize variety of substrate coming in treatment plant. Thus, even if they are detected in the range of 1011 to 1012 cfu/ml will not contribute to effective treatment of incoming waste.

According to one of the researches carried out for 12 municipal wastewater treatment plants having different treatment processes, using 454-pyrosequencing technology they found nearly 202,968 effective sequences of the 16S rRNA gene. This indicates that all the samples investigated represented the vast diversity of the microbial communities. Proteobacteria was found to be the dominant phylum in some samples, in other samples it was Bacteroidetes (Hu et. al., 2012; https://doi.org/10.1016/j.biortech.2012.04.061). Such kind of details, will give insight to professionals to redirect community structure to get more diverse and efficient. At times, using simple techniques like microscopy even gross idea of microbial community can be achieved. However, the correlation of such microscopic images with treatment plant health is under study by our research group.

The microbial community structure if studied in detail can lead to meaningful insights. Sludge bulking is one of the major issues encountered in winters by treatment plants. When a research group focused on the microbial community analysis, they found presence of 36 phyla, 293 families, and 579 genera in four WWTP activated sludge samples.

In case of wastewater, microbes can be either in suspension or in attached form. However, in both cases there are billions of organisms and thousands of species contributing to community structure. These communities are built according to the environmental conditions and substrate available. The relative abundances of Saprospiraceae, Flavobacterium and Tetrasphaera with the respective averages of 12.0%, 8.3%, and 5.2% in bulking sludge samples were higher than those in normal samples. Presence and high percentage of Filamentous Saprospiraceae, Flavobacterium and Tetrasphaera was the main cause for the sludge bulking (Xu et. al., 2018; Volume 2018, Article ID 8278970, 8 pages https://doi.org/10.1155/2018/8278970).

The composition of a microbial community and the abundance of its members also indicate functional capacity of treatment plant community. When we can identify the abundant bacteria present in the wastewater over all seasons, it can be then augmented to take care of difficult pollutant (Zaveri et al, 2015). In that study, 9 CETPs were studied for long period of time and the functional community diversity analysis was conducted. Highly even community structure and rich diversity of microbes were found to contribute to efficient treatment of the plants.

The major parameters which influence microbial community compositions are pH, dissolved oxygen, concentration of contaminant and various nutrients. As we all know it is difficult to take care of influent quality due to practical field conditions. In such conditions, if microbial community is supplemented with additional nutrient which has suppressive effect (but not killing effect as antibiotic) will lead to immediate response of species survival. For example, at times higher levels of phosphate can divert microbial metabolism to other direction, which can be compensated by addition of additional ammonical nitrogen.

The microbial community doesn’t form on the day of commencement of plant. That is why we see the lag phase in achieving treatment efficiency. Also, once formed it is not expected that community will not phase succession, they do go through succession on various levels and at various seasons. Although most plants if they have diverse resilient community structure will be able to withstand shock loads. It would be important to notice that if the most abundant strain is isolated and kept constant via augmentation, will lead to lesser incidents of loss of microbial community.

Detailed studies in terms of composition of microbial community structure should be incorporated in plant functionalities will save us from fear of genetically engineered organisms and unwanted outbreaks. Such novel approach would help us to develop innovation based on biologically profound fundamentals and will be safer for filed applications.

Contribution of Healthy Microbial Community and Impacts

Dr. Purvi Zaveri