Talibon Slaughterhouse Wastewater Retrofit
Talibon is a first class municipality in the province of Bohol located on the Northeastern coast of the Philippines. It is known for the Danajon Bank, which is Asia's only double barrier reef ecosystem. This area of extreme biodiversity is located within the inland Camotes Sea and boasts an exceptionally high number of coral and mangrove species.
Recognizing the extreme importance of this area, the Talibon municipal government is engaging in a host of environmental initiatives to reduce pollution entering the sea. In addition to a sanitary landfill project, two wastewater improvement projects are in the works. The first, the subject of this post, is to retrofit the wastewater system serving the new slaughterhouse so that the effluent discharge is fully compliant with the standards set by the Department of Environment and Natural Resources.
Contents
The New Slaughterhouse
The new slaughterhouse was constructed in 2008 to replace the old structure that was located right on the coast. The new construction was an effort to reduce the direct discharge of wastewater into the sea. The new facility has a modern design, which will make it easier for the operators to implement slaughterhouse best management practices.
Volume and Design Flow
an effort to estimate the design flow for the facility, records wereIIIIv IIn September 2007, an average month, the old slaughterhouse used 156 cubic meters of water and processed an average of 2 cows and 10 pigs per day, which equates to an average of 5.2 cubic meters per day of water consumption. Using this as a baseline, projections for water consumption for the new facility can be estimated. The new facility is designed for a production capacity of 10 cows and 50 to 100 pigs per day, or approximately 5 times the production of the existing facility. This would result in water consumption of approximately 26 cubic meters per day, assuming that September is an average month and that water consumption at the new facility would be linearly proportional to the existing facility. Using a waste conversion rate of 85%, the design flow for the wastewater system should be around 22 cubic meters per day. It is suggested that during peak processing seasons, the old slaughterhouse might be used to accommodate the excess work.
The Existing Wastewater System
The system as it is currently installed includes a single chamber digestive tank followed by two open concrete lined pits.
The facility layout is represented in the diagram. The left-most box represents the digestive tank, the middle box represents the first open pit, and the right-most box represents the second open pit. The main concern with the existing layout is that it appears to be too small to accommodate all of the flow and provide the required treatment. Biodigesters that are designed to accomplish anaerobic digestion of slaughterhouse wastewater are generally designed for detention times of between 7 and 14 days. Therefore, it appears that the digestive tank is significantly undersized to accomplish complete anaerobic digestion at the design flow. The pits are also on the small size given the projected wastewater flows. They will operate as anaerobic pits, which also require a sufficient detention time to accomplish proper treatment.
Wastewater Treatment Concerns
There are two major concerns that are driving the initiative to retrofit the wastewater system:
- The first concern is the inability of the wastewater system to meet discharge requirements for biochemical oxygen demands and total suspended solids. Based on the components installed and the anticipated strength and volume (loading) of the wastewater, it is likely biocehmical oxygen demands and total suspended solids will exceed discharge limitations.
- The second concern is odor and nuisances. Anaerobic wastewater systems that are open to the atmosphere often generate odors and mosquitoes.
An initial recommendation is to minimize waste. Since the wastewater treatment infrastructure is already installed, reducing the volume and strength of the wastewater to be treated to match the infrastructure is one option. The facility should also follow best practices. For example, collecting the blood and offal from the slaughtering operation will help reduce organic loading and waste volume, making the wastewater easier to treat. In addition, covering the influent channel will minimize rainwater entering the system, which will maximize wastewater detention time through the system.
Infrastructure Retrofit
In addition to the above suggestions, some retrofitting of the existing system may be beneficial. Engineers for the municipality are considering installing baffles in the settling tank to help improve the settling efficiency. Lining the ponds would also provide some protection to the groundwater. Additionally, installation of a planted gravel filter is being considered to polish the wastewater effluent prior to discharge.
Next Steps
The following next steps are recommended to move the project along:
- Finalize the design details for the retrofit. Review the sizing calculations to verify that the design meets the minimum requirements for sizing of the various components of the system. Work with engineers at the Bohol Environment Management Office during the sizing review.
- Prepare a materials list and cost estimate for the modifications.
- Prepare the findings in a proposal format that includes the detailed designs, cost estimate and recommendations. Present this to the Mayor.