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Anaerobic single baffled reactor as an alternative domestic wastewater treatment system in Indonesia

Wibisono, Gunawan (2002) Anaerobic single baffled reactor as an alternative domestic wastewater treatment system in Indonesia. PhD thesis, Murdoch University.

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The conventional septic tank is an anaerobic wastewater treatment system commonly used worldwide particularly in developing countries. In Indonesia populations in urban areas are mostly served by septic tanks and in rural areas similar systems with lower efficiency are used to deal with the domestic wastewater. The implementation of sophisticated wastewater treatment systems for developing countries such as Indonesia is likely to cause major issues due to its huge cost and requirement of skilled persons in operating and maintaining such systems. The current situation is unsatisfactory and leads to water resources deterioration. It is therefore a challenge to find methods to improve the performance of the conventional septic tank system without neglecting its simplicity of construction and operation to suit the conditions of developing countries.

One of the main requirements for anaerobic wastewater treatment system to operate effectively is the mixing between biomass and the incoming substrates. The conventional septic tank system does not provide this mixing. Therefore it generally results in a poor performance in treating domestic wastewater. This thesis presents a novel yet simple design of an anaerobic system for developing countries called the Anaerobic Single Baffled Reactor (ASiBR). A baffle is inserted in the septic tank system to force mixing between the incoming wastewater and the sludge in the tank.

Using tracer study the ASiBR system was tested for its hydraulic characteristics. Two trapezoidal shaped reactors were used to represent the septic tank and ASiBR systems. In the ASiBR it was observed that the tracer material was completely flushed out after three hydraulic retention times and the tracer recovery was more than 95%. In contrast in the septic tank system, dead spaces were physically observed and the percentage of tracer recovery was less than 70%. The results clearly show more effective contact between substrates and biomass in the ASiBR.

Experiments to investigate the response of the ASiBR to soluble and insoluble substrates (volatile fatty acids, glucose, insoluble cellulose and cooking oil) were conducted. The two trapezoidal shaped reactors were also used to test their performance in degrading volatile fatty acids (VFA). The ASiBR proved to be able to treat high concentrations of VFA, while the septic tank system showed very poor VFA removal even in treating fairly dilute feed. The ASiBR was able to degrade VFA three times higher in concentration than the septic tank.

The experiment with glucose was conducted using three reactors simulating the septic tank, ASiBR and upflow anaerobic sludge blanket (UASB) systems. The idea was to look at the performance of the ASiBR in comparison to the current popular anaerobic UASB system and the traditional septic tank system. Three cylindrical shaped reactors were built in order to include the UASB system and they were run simultaneously for glucose degradation trials at various concentrations. The results show that the ASiBR was able to degrade glucose at concentrations of nearly two times higher than in the conventional septic tank system. The biomass activity in the ASiBR was comparable to that in the UASB system.

The tendency of the ASiBR to behave as a two-stage reactor system was observed when the ASiBR was fed with insoluble cellulose and canola oil. It was found that the pH in the first compartment was lower than the pH in the second compartment. It appears that the acidogenic and methanogenic groups of bacteria were separated by the baffle, which formed a more stable system to handle pH fluctuations within the reactor.

In conclusion, the overall results show that the single baffle insertion in both designs, rectangular and cylindrical, was able to improve the performance of the septic tank. For further research, it is recommended to conduct the experiment with a baffle, which has around 50 to 70° bend at the down end for 50 to 70 cm. This should promote better mixing. The new system needs field trial before implementation.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): Division of Science and Engineering
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: Thank you.
Supervisor(s): Ho, Goen
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