- City Wastewater Facilities
Like the water management plants, wastewater facilities are also large consumers of energy and thereby large emitters. Opportunities exist at various levels in the treatment process to reduce emissions. The contact person for the City’s wastewater facilities was the same engineer as for the water treatment facilities and he provided an overview of the process. The City owns and operates two waste water treatment facilities- the North Durham Wastewater Reclamation Facility (NDWRF) and the South Durham Wastewater Reclamation Facility (SDWRF). The main treatment is biological nutrient removal process that removes ammonia, nitrogen, nitrates and phosphorus. This involves primary clarification including passing the water through digesters and compaction. A considerable amount of energy is required for this stage. The next step is aeration. Next, the water is passed through blowers and then passes through secondary clarification. Some of the water is recycled at this stage. The final step is tertiary treatment where ultraviolet rays are used to disinfect the wastewater. Then the water is finally pumped out (Senior Engineer 2013).
- County Wastewater Facility
The official from wastewater department, who is in charge of the county water treatment upgrades, explained waste water treatment processes and the upgrades that the county has done in the wastewater management facilities since 2006. The most plants were built in 2005. There have been operational improvements since 2006. The facility has saved energy by reducing the number of running oxidation dishes. For example, only two rotors are operated out of four rotors at night. Another major upgrade in terms of energy saving aspect was installing a new sludge facility on February 2013. The wastewater was previously transported to a lagoon which creates odor. The new sludge facility saves energy by not re-treating the wastes and dries the wastes, which reduces smell and cost since the wastes are paid by the amount of load. The estimated cost of energy saving was 10%. This facility cost about 10.7 million dollar. Another noticeable aspect for the waste treatment facility is that all buildings are LEED certified, and most energy costs are from water treatment facilities. In the future, the department considers introducing a new sludge facility, which is a solar drying sludge. This is a concrete facility, which uses solar energy to dry sludge by installing greenhouse drier in the plant. The amount of dried sludge shipped would be 3 trucks a week instead of 10 trucks a week. This will cost 15 million with 10 year capital plan (Utility Division Manager, 2013).