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Introduction to Decentralized Wastewater Management
Ligy Philip
Department of Civil Engineering
IIT madras
Introduction
Decentralized wastewater systems collect, treat, and reuse or dispose of wastewater at or near its point of generation.It include systems that treat wastewater from individual homes or buildings as well as cluster systems that treat wastewater from groups of two or more houses.Unlike centralized urban wastewater treatment systems, decentralized systems treat wastewater close to the source, typically using small pipes for collecting small volumes of domestic wastewater.
Most cost-effective option esp in rural areas and hilly terrain.
Cost-effectiveness depends on a number of factors like population size and density, topography, distance to an existing centralized system
Introduction (Contd..)
Often more affordable for small communities
Achieves high removal rates for most pollutants
Less hydrological impact
Can be integrated into a flexible wastewater
system
Can be used as a tool to manage development
Advantages of DecentralizedWastewater Treatment
Disadvantages of DecentralizedWastewater Treatment
Potential threat to ground water quality
Can be harder to document treatment
effectiveness
No dilution benefit
Risk of failure concentrated
Requires greater awareness and participation of
homeowners
Less familiar to engineers
Funding challenges
Lack of management structures
Fragmented regulatory structure
Disadvantages of DecentralizedWastewater Treatment
Barriers to Implementation Lack of Knowledge and Public Misperception
Homeowners and developers think that houses with centralized systems will carry higher property values and have greater acceptance
Legislative and Regulatory Constraints
Lack of Management Programs Liability and Engineering Fees Unwillingness of homeowners and developers to accept the liability associated with unfamiliar treatment systems
Financial Barriers The funding agencies generally do not assist privately owned systems.
Decentralized Wastewater Treatment
Reduce sewer networks Simplify sewer by applying SOLID-FREE
SEWER Involve local labour and material available Construct what requires low maintenance and
no energy Generate water and nutrients for irrigation in
agriculture and food-garden
Effective O & M
Properly constituted and staffed DWM [RME] districts and agencies have proven to be an effective means of assuring the long-term performance of onsite [decentralized] systems.
Prince and Davis, 1986
Vision Statement
Large-scale decentralized wastewater management systems should be allowed only if a responsible management agency [district] has been designated.
Crites & Tchobanoglous, 1998
Successful Responsible Management Entities (RME) must include a legal entity that has the technical, managerial, and financial capacity to ensure the viable, long-term, cost-effective, centralized management, operation, and maintenance of decentralized wastewater systems in accordance with appropriate regulations and generally accepted accounting principles.
- Yeager and English, 2001
The EPA reports
Decentralized systems are used in 25% of US homes and the percentage is increasing
Decentralized is a permanent part of the Nations wastewater infrastructure
More than half of all septic systems are more than 30 years old and at least 10% experience a failure every year
Adequately managed decentralized systems are a cost effective long term option for meeting public health and water quality goals
Local governments need a flexible framework and guidance to tailor their management programs to the needs of the community and watershed
Five Management Models
Model 1 - Homeowners Awareness Model 2 - Maintenance Contracts Model 3 - Operating Permits Model 4 - Responsible Management Entity
(RME) Operation and Maintenance Model 5 - RME Ownership
Model 1 - Homeowner Awareness
Individual OSSF owned and operated by homeowners
Use in areas of low environmental sensitivity Treatment technologies limited to
conventional systems Maintenance reminder notification
Model 2 - Maintenance Contract
Homeowner system ownership Professional maintenance Complex OSSF design such as ATU Licensed technicians provide proper and
timely maintenance Individual contracts with individual
homeowners
Model 3 – Operating Permits
Annual permit renewal to assure system performance
Suitable for increased environmentally sensitive areas
Performance based designs with management controls similar to Model 2
Individually owned OSSF systems
Model 4 – Responsible Management Entity Operation and Maintenance
Decentralized systems May be combined with individual OSSF systems Highly reliable operation and maintenance Water quality and sensitive environmental areas Operating permits are issued to the RME instead of
individual homeowners
Model 5 – Responsible Management Entity Ownership
Suitable for decentralized systems Not suitable for individual OSSF’s Systems are owned, operated and maintained by the
RME Removes property owners from responsibility for the
system Greatest assurance of system performance in the
most sensitive of environments
Functions of RME Districts
Asset Inventory System design and installation Plan review & construction inspection Operation and Maintenance Inspections Notification Certification Monitoring Reporting Education
Successful RME Attributes
Governance capacity Technical capacity Managerial capacity Financial capacity
Governance Commonalities
Well defined mission, objectives and goals Sufficient political will exists Preexisting laws sufficient to grant the RME authority to
accomplish it’s mission, objectives and goals Operation outside traditional health department paradigm Big picture focus and NOT micromanagement Set fees and price structure
Technical Commonalities
Biological unit processes Chemical unit processes Mechanical unit processes Component uniformity System type and compatibility
Managerial Commonalities
A paid manager Effective and timely collection enforcement Strong board, annual performance reviews Use generally accepted accounting principles and
good record keeping Strong team of professional consultants Long term and contingency plans
Financial Commonalities
Long-term financial planning Sufficient cash flow to be self-sufficient Establish reasonable and sustainable monthly
charges Independent financial oversight Funds escrowed monthly for replacement
cost Annual audit and performance review
Recommendations for RME’s
Existing development using existing treatment systems – Model 3
Existing development using new treatment systems – Model 4
New development using new treatment systems – Model 5
START
Define Service Area
Determine number of Connections
Sufficient political will exist
Existing laws in place to provide sufficient legal
authority to the new RME
Petition for RME creation and authorities
Develop mission objective &Goals
RME Startup
STOP
Select RME legal structure
Develop required technical, managerial and financial capacity
Develop short and long term plans and Contingencies
This chart makes certain assumptions regarding the
service area and system size, age an type
Continue
Continue
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Closing Comments
As the ethic of professionalism continues to grow within the industry, there will be an acceleration in the formation of new RME’s. These RME’s can bring tremendous benefits to rural and semi-urban areas by providing effective and efficient wastewater service that protects the public health and environment at an acceptable price.