Influence of Substrate to Biomass Ratio (F /M) and pH On Microbial Stability of Activated Sludge

Activated sludge contains biological floes composed of bacteria that degrade the organic
matter in the waste water for its growth. The microbial stability of the activated sludge
represented by the characteristics of the floes. Project is focused on activated sludge used by
most operating wastewater treatment plant owned by PETRONAS. Bacteria chosen will be
BIOCHEM (BCI-103) brand. The bacteria are taken from a gas processing plant located in
Kerteh, Terengganu.
The main objective of this project to study on the influence of two major parameters in
wastewater, which are the substrate to biomass ratio or also known as food to microorganism
(FIM) and pH, to the characteristics of the bacteria floes. Optimum value of F/M and pH
obtained from this project will be recommended to further enhance the wastewater process
control at the processing plant. Besides that, the characteristics of floes that obtained at different
F 1M and pH can be served as informative data to further enhance the understanding of the
bacteria used.
Nowadays, with the increasing industrial activity, usage of hazardous chemicals escalates
thus endangering the environment. News raised on the environment pollution especially the
water pollution effecting the seas and rivers. One of the main causes of this pollution is the
ineffective operation of wastewater treatment plant. Many microbially-related activated sludge
solids separation problems occurred such as dispersed growth, filamentous bulking and foam
formation. Existing design parameter such as sludge age, Chemical Oxygen Demand (COD), and
Sludge Volume Index (SVI) can't predict the stability of the bacteria floes. These design
parameters are more oriented to the final goal of releasing effluent below the standard limit set
by the government. Thus, the project will focus on the study of F/M and pH as design parameters
and their influence to the bacteria floes.

The scope of study for this project contains three elements which are the F 1M, pH, and
the microbial stability of the activated sludge. With others parameters such as temperature,
Mixed Liquor Suspended Solids (MLSS), and sludge retention time (SRT) set constant, F/M and
pH are manipulated to obtained the results. Microbial stability of activated sludge is judged by
the characteristics of bacteria floes. Activated sludge is stable when microorganisms to stick to
each other and to nonbiological particles as sludge floes (Jenkins et al.,2004). Increase size of
floc diameter indicates the sludge is stable and at optimum condition. Activated sludge is
populated by all kinds ofbacterias. However, to study the microbial stability for this experiment,
six species were chosen which are amoebae, flagellates, free swim ciliates, crawling ciliates,
stalked ciliates, and rotifer. The abundance of these species are found and analyzed as each
species has its own function and indication for the condition of sludge.
Research starts by searching for any other relevant journal or article published by othf;lr
researches and from there, the results would be review and useful information will be summarize
and taken as an information to this research. Next, contacts are made with the industry personnel
in order to obtain the sample bacteria and knowledge of the activated sludge system used in the
plant. Then, research progress experimentally in the laboratory and the results gained are
discussed and documented.
Findings from this project show that the microbial stability of activated sludge is
influenced by F 1M and pH. Under different F 1M and pH conditions, bacteria floes particles and
sizes are different. Under microscope, bacteria population is analyzed and documented.
Efficiency which is calculated by the removing percentage of the (COD) is plotted. Further
findings are discussed in latter part of this dissertation.