Company ProfileCase Study: Tannery—Queensland, Australia
The Problem
A tannery was discharging highly polluted effluent onto land with its associated foul odors, resulting in numerous complaints. There was evidence of pollution of the water bearing strata beneath the land. Excessive levels of chromium were also a problem.
The EversTech Solution
Recommendations made by the EversTech team about basic "housekeeping" practices reduced chromium levels very significantly. EversTech developed a special bio-culture, tolerant of chromium, for use in the digestion system.
With a heavily polluted effluent at an average flow rate of 150 m3/day, EversTech recommended anaerobically pre-digesting the waste water in a totally closed system, thereby recovering the methane for use in the boilers. The final biomass produced by the process could be recycled into the existing de-watering filter and then into a drying system to produce fertilizer.
The supernatant liquor from the anaerobic digestion process would receive final treatment by chemical flocculation and clarification in the existing treatment system, followed by secondary aeration and lagooning.
Basis of Design—Analysis of Effluent
| pH Value | 6.5–7.5 |
| Chromium | 450 mg/l |
| Suspended Solids | 14,000 mg/l |
| Total oil and grease (Average) | 2,000 mg/l |
| Chemical Oxygen Demand (Average) | 50,000 mg/l |
| Biochemical Oxygen Demand (Average) | 30,000 mg/l |
| Flow Rate | 15–30 m³/hr (150m³/day) |
| Temperature | Ambient |
With little modification, the existing system was converted to a bio-flocculation process, and with the use of the bio-augmentation cultures, the necessity for chemical flocculation was eliminated, incorporating an aerobic stage by use of the existing lagoons.
Capital cost of the treatment plant—£400,000.
Operating Costs—Annual
| Labor | £20,000 |
| Electricity | £42,000 |
| Bio-cultures | £42,500 |
| Maintenance—1% of Capital Cost | £40,000 |
| Total | £144,500 |
Financial Benefits
Recycled Water
The effluent is of such quality that at least 90% of it is recycled.
Value = £67,500/yr.
Solids Recovery
The surplus biomass and settled solids removed from the clarifier, when combined, provide a dry solids production of approximately 2 tons/day. This can be sold as a 6–7% nitrogen fertilizer with an approximate value of £150,000 per year.
Energy Recovery
The anaerobic digestion is operated mesophyllically; the yield of biogas is approximately 3,750 m3/day. This is equivalent to 2.22 tons of oil/day with an approximate value of £266,500 per year.
| Water | £67,000 |
| Biomass | £150,000 |
| Energy | £266,500 |
| Total Income & Savings | £484,000 |
| Total Operating Cost | £144,500 |
| Total Net Benefit | £339,500/yr |
Environmental and Community Relations Benefits
- No odor from the treatment plant.
- Reduction in water usage by recycling.
- Minimization of the environmental impact.
- Improved public relations.