PERFORMANCE OF A GRANULAR ACTIVATED CARBON BIOFILTER IN LOW STRENGTH WASTEWATER TREATMENT D. S. Chaudhary, H. H. Ngo and S. Vigneswaran Environmental Engineering Group, E. E. R & D Laboratory, Faculty of Engineering, City Campus, Building 2, Level 6, University of Technology, Sydney, P. O. Box 123, Broadway, NSW 2007, Australia

INTRODUCTION  Any conventional filter with attached biomass growth on the filter media is known as BIOFILTER.  Biofilter can be used in both Water and Wastewater Treatment efficiently.  GAC biofilter is often used in tertiary wastewater wastewater treatment and water treatment.

INTRODUCTION Contd……  Biofilter is the only economical biological treatment option in the tertiary wastewater treatment.  Biofilter is also economical and environmentally friendly solution in treating wastewater of relatively small volume e.g. from hotel or small communities.

INTRODUCTION Contd……  In tertiary wastewater treatment, biofilter can remove nutrients and dissolved organic substances and produces effluent of high quality for reuse purpose.  In water treatment, it can remove pollutants such as biodegradable and synthetic organic materials that procure odor and taste and cause microbial regrowth in water distribution pipelines.

Constituents of the Wastewater Used

Materials and Methods Filter column of diameter 2 cm and height 50 cm was employed The column had ports for influent feed, effluent collection and backwashing. The column was packed with 5 g of GAC (bed depth 4 = cm, porosity = 0.65, particle surface area = 1104 m 2 /g, effective particle size = mm)

Schematic Diagram of the experimental Set-up For the Biofilter P Stock Solution of Synthetic Wastewater Valve Pump Constant Head Overhead Tank Influent Feed Effluent out Valve Backwash Water in Backwash Water out Stainless Steel Mesh Biomass attached on GAC Pellet Filter Column (dia. 2 cm) Overflow Line Port with Valve

Material and methods contd.……. Constant pressure head was maintained to keep a constant filtration rate of 1 m/h. The filter was backwashed at 30% bed expansion for approximately 5 minutes every 24 hours of filter run. Total organic carbon (TOC) was measured using UV-persulphate TOC analyser (Dohrmann, Phoenix 8000).

Material and methods contd.…… Total adsorbed biomass as dry weight was calculated every week. The synthetic wastewater was prepared everyday and the filtration was run continuously for 77 days.

Results and Discussion TOC contribution of Glucose, Peptone and Yeast extract with inorganic compounds was 79%, 11% and 10% respectively. Biodegradation of organic substances suggested that fresh synthetic wastewater solution need to be prepared everyday for filter influent.

Biodegradation of Organics of Synthetic Wastewater Used

Performance of the GAC Biofilter (Average influent TOC = 3.5 mg/L, Bed depth = 4 cm, Filtration rate = 1 m/h)

Biomass Growth in the GAC Biofilter (Average influent TOC = 3.5 mg/L, GAC = 5 g, Filtration rate = 1 m/h)

Results and discussions contd.……. Minimum biomass of g per g of GAC was observed after 63 days of continuous operation. Another set of operation conducted at 2.5 m/h filtration rate showed a biomass growth of 0.1 g per g of GAC in 30 days. The decrease in biomass during 7th to 9th week of operation may be due to die- off of microorganisms and its subsequent removal in backwashing

Effect of Filtration Rate on the Performance the GAC Biofilter (Acclimatization period = 77 days, GAC = 5 g, average influent TOC = 3.5 mg/L)

Effect of Influent Organic Concentration on the Performance the GAC Biofilter (Acclimatization period = 77 days, GAC = 5 g, Filtration rate = 1 m/h)

CONCLUSIONS  GAC biofilter can effectively be used to produce better quality of effluent for wastewater reuse purpose.  The biological activity led to consistent organic removal efficiency over a long period of time.  The daily backwash adopted did not seem to affect the biological mass growth thus effluent quality.

Conclusions contd.……  Further works on the different concentration and composition of attached biomass are necessary for correct evaluation of the biofilter.  Further works with real wastewater are also necessary for its practical application in the field.  A correct choice of filtration rate and filter bed depth is necessary for long-term operation with consistent and superior effluent quality.