Water Pakistan

COMPARISON OF AEROBIC AND ANAEROBIC WASTEWATER TREATMENT

By

Hira Waheed

(07-arid-1088)

A thesis submitted in partial fulfillment of

the requirements for the degree of

Master of Science

in

Environmental Sciences

Department of Environmental Sciences

Faculty of Forestry, Range Management and Wildlife

Pir Mehr Ali Shah

Arid Agriculture University Rawalpindi,

Pakistan

2009

ABSTRACT

Water is a basic necessity and is required to run all industrial, domestic and agricultural activities. With an increase in its consumption rate, quantity of wastewater generated on daily basis has also increased. Wastewater handling and it’s conversion into useable form by an effective treatment has become a major challenge of recent era and it needs to be treated because it contains toxic and persistent chemicals and can be a threat to environment if remain untreated. Biological treatment is an environmental friendly technique with its low operational and capital cost. It includes aerobic and anaerobic processes both of which have low energy consumption and low sludge production, thus making biological treatment most suitable. This study was conducted to evaluate the effectiveness of hydraulic retention time (HRT) on activated sludge process (ASP) and up flow anaerobic sludge blanket (UASB) process. Experimental condition i.e. HRT was varied and the effluents were evaluated in terms of pH, color, chemical oxygen demand (COD), total dissolved solids (TDS), total suspended solids (TSS) and alkalinity. Reactors in continuous flow mode were operated to treat the wastewater. In the treatment varying concentration of HRT was used in different combinations i. e. 2, 4, 6, 8 and 10 hours for aerobic process and 4, 8, 12 and 24 hours for anaerobic process. In ASP, maximum color and COD removal efficiencies of 69 and 60 percent were achieved at HRT of 8 h in case of domestic wastewater treatment.  However, in combined wastewater treatment, optimum color and COD reduction approached 72 and 66 percent at HRT of 24 h in case of UASB process. The results have demonstrated that the color was mainly removed under anaerobic conditions while COD was reduced under aerobic conditions.

SUMMARY

The recent developments in industrial, agricultural and commercial sectors are important causes of high water consumption resulting in large quantity of used water being produced and rejected. In developing countries, where access of safe drinking water is not guaranteed for a majority of the population, it is of great importance to maintain the quality of surface water sources. So there is an urgent need to develop technologies to treat huge volumes of wastewater in shortest possible time frame. Biological treatments like activated sludge process (ASP) and upflow anaerobic sludge blanket (UASB) are widely used in wastewater treatment plants to reduce effluents levels in contaminated wastewater originating from both the municipal and industrial sectors.

Wastewater used for this study was obtained from domestic, industrial and combined wastewater stream drain from I-9 Islamabad. This study was conducted to evaluate the effectiveness of hydraulic retention time (HRT) on different types of wastewater by applying ASP and UASB process. ASP occurred in two units. An aerated biological reactor, in which microbial activity was used to degrade pollutants, and a settling unit, in which activated sludge settled at the bottom of the unit. While, UASB consisted of an upflow of wastewater through a dense sludge bed with high microbial activity. Experimental condition i.e. HRT was varied and the effluents were evaluated in terms of pH, color, COD, TDS, TSS and alkalinity.

Following conclusions were drawn from the study:

• In case of ASP, at retention time of 6 h, 57, 62 and 35 percent of total COD removal was obtained for domestic, combined and industrial wastewater respectively.
• For domestic, combined and industrial wastewater, UASB rector achieved 52, 53 and 10 percent COD removal at retention time of 12 h.
• Comparatively, aerobic treatment efficiently removed COD value within very short period of time than anaerobic process.
• Color was mainly removed under anaerobic conditions while COD was reduced under aerobic conditions.

Based on these results, it is recommended that

• For the treatment of a combined industrial and domestic wastewater, use an integrated system consisting of a UASB reactor followed by the ASP to produce a good effluent quality.
• An extensive study is suggested to assess the effect of the process conditions such as temperature, sludge granulation, sludge height, organic loading rate (OLR) and mixed liquor suspended solids (MLSS) on the removal efficiencies of UASB reactor.
• Further more; the biogas generated during anaerobic process adds attraction as it can be used as fuel.