Rural Wastewater Management Practicesin USA and Other Countries

Prepared by:

Peter Haase, MS, PE

Fall Creek Engineering

Presentation Outline

• Small community and decentralized wastewater management

• Status of rural wastewater management in US and other countries

• Factors to consider in small wastewater management project

• Wastewater treatment technologies

• Approaches to rural wastewater management

Difference between centralized system and decentralized system

Centralized WWTS

• Centralized systems serve high density urban areas

• Typically population served >10,000 people

• Centralized systems typically use complex and advanced treatment technologies to reduce BOD, TSS, Nutrients, and pathogens (disinfection commonly used)

• Centralized systems typically discharge to surface water (rivers, bays and oceans)

• Water recycling/reuse becoming more widely practiced in response to water scarcity

Decentralized WWTS

• Used in rural or low density development areas

• Typically small communities <10,000 people

• Simple biological treatment systems to reduce BOD, TSS, and nitrogen. Occasionally, pathogen reduction using waste stabilization ponds or disinfection

• Discharge to land disposal system is most common

• Reuse with subsurface drip irrigation is very common in USA

Small Community and Decentralized Wastewater Management

• Typically systems serving under 10,000 people.• Located in rural or remote location• Infeasible to connect to a larger centralized publically owned wastewater

treatment works (POTW)• Typically use simple wastewater treatment systems and land disposal systems

• Three Common systems:1. Small/Rural Community systems with sewers, wastewater treatment system, and land

disposal system2. Decentralized community systems using community septic tanks and land disposal system3. Individual onsite wastewater systems (septic tanks and drainfields)

• Type of System selected based on several factors:1. Community layout2. Housing density3. Terrain (topography)4. Financial Constraints5. Political Constraints

Rural Wastewater Influent Characteristics

• Wastewater characteristics dependent on activities in the community:– Typically domestic wastewater (black and graywater)– Level of water service will influence quality of wastewater:

• Low level of water service most water will be toilet water and may be more concentrated• High level of service may be more diluted due to higher water usage for showering,

laundry water

– Artisan businesses can have a significant influence on influent quality (ex. Mescal production in rural Mexico can raise BOD levels very high in rural villages)

– Holiday’s can also influence wastewater quality and flows in rural villages

• Influent quality can be highly variable for all of these reasons

• Common values observed:

• Low Strength Wastewater: BOD & TSS ~150 mg/L, NH3-N = 30 mg/L

• High Strength Wastewater: BOD & TSS ~300 to 500 mg/L, NH3-N = 40 to 60 mg/L

Performance Standards

• Generally three types of standards

– Water quality based – protective of resource

– Performance based – technically achievable by treatment systems

– Regulatory based – combination of water quality and technically based standards

• Standard for land disposal of treated wastewater:– Reduction of organic matter and solids to not clog soils:

• BOD & TSS <30 mg/L

– Reduction of total nitrogen to protect surface and groundwater:• 50% to 80% reduction of total nitrogen based on public health risk

• 90% reduction to protect pristine surface water sources – eutrophication

– Reduction of Pathogens in subsurface disposal system• Require adequate depth of soil & separation to shallow groundwater

– Typically 1 meter of soil minimum

Presentation Outline

• Small community and decentralized wastewater management

• Status of rural wastewater management in US and other countries

• Factors to consider in small wastewater management project

• Wastewater treatment technologies

• Approaches to rural wastewater management

Rural Wastewater Treatment Standards for Land Disposal Systems

• USA– State of California – Central California Coast Region

• Standard is loading based (40 grams/acre of total nitrogen) to protect groundwater quality from nitrate pollution

• Presently considering new standard for enhanced treatment units: BOD & TSS < 15 mg/L; TN < 10 mg/L

– Local Jurisdiction - County of Santa Cruz (most advanced county in State of California

• Performance and Water Quality Based Standard: • BOD and TSS < 30 mg/L• 50% reduction in TN

• Japan– Performance based standard:– BOD < 20 mg/L

• Australia/New Zealand– Performance Based Standard:– BOD <30mg/L – TSS < 20 mg/L

[Note: Difficult to find established standards for land disposal of wastewater]

Status of Rural Wastewater Management in US and Other Countries

Technology– In US and other developing countries there are a lot of different commercial available enhanced treatment

systems– Emerging market for new technologies and water recycling driven primarily by the green economy and water

scarcity issues not necessarily water quality/public health issues– Limited quality control or verification of technologies – buyer beware

Administrative– Most jurisdictions have good programs developed for simple conventional septic systems– Oversight and administration of Rural and Decentralized wastewater management programs are commonly

underfunded and run with limited and poorly trained staff who have limited resources– Need for ongoing training for engineers/designers– Better tracking, monitoring and evaluation of projects – many projects built , but rarely checked for

performance and commonly system is abandoned or not maintained

O&M– The biggest challenging facing the rural/decentralized wastewater management program is operation and

maintenance of the systems– Lack of trained operators or service providers– There are good public and private models

• Public model – formation of local wastewater management district to manage many systems or many small community• Private sector model – Creation of a approved service providers by local or regional authority who can be hired directly by

individual homeowner or community to manage system

Water Quality– Regional coastal, lake, bay and groundwater monitoring programs on the east and west coasts of US have

documented long-term water quality problems attributed to decentralized wastewater disposal – requiring enhanced treatment technologies

– Some successes reported over the past several years in Central California Coastal area – reduction in nitrogen, reduction in pathogens

– Need for better coordination of projects and monitoring programs

Presentation Outline

• Small community and decentralized wastewater management

• Status of rural wastewater management in US and other countries

• Factors to consider in small wastewater management project

• Wastewater treatment technologies

• Approaches to rural wastewater management

Factors to Consider in Developing Rural Village Wastewater Projects

• Community support and administration

• Sustainability and Reliability

• Costs and Energy

Community Support & Administration

Introducing technology to rural community important factors to consider:– Education of population

– Interest of population - ownership

– Perception of population – Is there a perceived problem to solve?

– Who will administer and manage project?

– Do they have the skills to administer the project?

– Will they pay for the service?

– How much will they pay for wastewater treatment?

– Do they have water availability problems?

– Will they reuse the water if it is well treated?

– Consider project as water reclamation instead or waste management – build in true value and benefit to the community

– Environmental education opportunity – collaboration with local schools

Sustainability/Reliability• Keep in mind that wastewater treatment systems are machines that require constant operation and maintenance

no matter how simple.

• Minimize electro-mechanical equipment (motors, blowers, pumps)

• Use passive treatment systems (gravity flow systems)

• Design with redundancy and maintenance in mind

• Use local labor to construct and maintain – local ownership and knowledge

• Easy to operate and maintain

• Project will be sustainable if it works for the useful life (>30 years)

• Minimize nuisance conditions (primarily odors)

• Consider water resource recovery not waste management

• The trend in the sector is the production of Carbon Neutral Water - minimize the carbon foot print of the project

• Land Banking. Many projects we want to consider growth and land availability/accessibility – land based treatment systems afford greater long term opportunities by securing and retaining land than compact high rate systems built in small spaces that do not provide for future growth.

• Project Value and End of Life Cycle. Land based treatment projects may actually appreciate over the 20 year life cycle period , where as small high rate systems on limited land area will likely depreciate over the 20 year period.

Capital Costs• Land based treatment (ponds and

wetlands) is usually the least-cost solution if land is available

• Passive gravity flow treatment units

• Combined unit processes to reduce size in limited areas

• Use of local or regional materials

• Minimize electro-mechanical equipment to the extent practical

Energy– Attempt to use gravity and not

electricity

– Is there a reliable source of energy?

– Will the system require electrical energy?

– Will you need backup power?

– What will the power costs be?

– Will the village continue to operate the system if the energy demand is high?

– Energy Efficiency important to minimize carbon foot print

– Opportunity for renewable energy source of power if electricity required

Presentation Outline

• Small community and decentralized wastewater management

• Status of rural wastewater management in US and other countries

• Factors to consider in small wastewater management project

• Wastewater treatment technologies

• Approaches to rural wastewater management

Small Community Sewer Collection SystemsThree common types:

1. Conventional gravity flow sewer systems2. Small bore sewer systems3. Solids free sewer or STEP sewer Systems

Conventional Sewers• Common to large urban centers• Pipe sizes usually 200 mm or larger• Meeting local and national standards• Relatively expensive to construct• Accommodate large flows

Small Bore Sewer• Designed for low or small flow applications• Adopted in many developing countries• Small pipe diameters found acceptable 100 to 150 mm• Lower cost solutions• Allow for more flexible design and layout in complex settings – ancient villages or peri-urban barrios or slums• Minimum cover requirements due to smaller pipe size• May need to use grit/grease traps to minimize clogging

Solids Free Sewers or STEG/STEP Systems • Variation of small bore sewers with the addition of septic tanks at individual homes or in community sewer systems to reduce

accumulation of solids in low gradient sewers• Add costs to systems• Access for tank maintenance is a constraint• Maintain the tanks is also very important

Rural Wastewater Treatment

• Decentralized Treatment Systems

– Individual or Community Septic Systems

– Pour Flush Latrines

– Individual Enhanced Treatment Systems

• Rural Community Wastewater Treatment Systems

– Pretreatment

– Primary treatment

– Secondary treatment

– Advanced secondary treatment

Pretreatment/Headworks

1. Screening – to remove debris and garbage

2. Grit Chamber – to remove sand and grit

3. Open channel flow measure – to regulate and measure flow into the plant

Poorly Designed and Difficult to Maintain Screen Ningbo, China

Typical Two-Stage Trickling Design

•Mechanical Plant

•Uses simple and redundant pumps

•Simple designs that can be manufactured with locally available materials

•Achieve high level of BOD, TSS and TN removal

•Compact design does not take much land

Screened Air Vents

Spray Nozzle

Random Media

Media Support

Combined Trickling Filter and Recirculating FWS WetlandSLVHS

– Design flow = 75 m3/d

– 0.15 HA

– Recirculating FWS (1:3 ratio)

– Influent BOD = 120 mg/L, Effluent BOD = <10 mg/L, % Reduction >90%

– Influent TSS = 60 mg/L, Effluent BOD = <5 mg/L, % Reduction >90%

– Influent TN = 120 mg/L, Effluent TN <20 mg/L, % Reduction >80%

Recirculating Sand/Gravel and Textile Filters

• Simple Design

• Require Relatively large area of land

• Uses small pumping systems

• Relatively low maintenance cost

• Sand/Gravel bed replacement ~10 years

• Textile filters long life – high costs

• Good Treatment Performance– BOD and TSS < 15 mg/L

– 50% Reduction of TN

Rural Wastewater Management Program Open Source Information System

• Once a Rural Wastewater Management Program is established recommend developing a tracking system to assess financial, managerial, technical and water quality aspects of projects

• South Africa has developed and implemented a Open Source Software electronic water quality data capture system (eWOMS) that can obtain and disseminate information and be used as a good management tool to provides real time water quality data to regulatory and management offices

• The system can be designed to provide the status of operations and water quality information. Audit information and water quality data is loaded onto eWQMS allowing for auto-reporting for legislative compliance and to demonstrate treatment plant efficiency to all stakeholders, including municipalities, provincial government departments, DWAF, and the Department of Health.

• The eWQMS can be used as a decision-making tool to identify areas of urgent need and the current threat to Primary Health and Environmental Health. The system allows for setting of priorities and distribution of resources for to remedy problems.

Presentation Outline

• Small community and decentralized wastewater management

• Status of rural wastewater management in US and other countries

• Factors to consider in small wastewater management project

• Wastewater treatment technologies

• Approaches to rural wastewater management

Rural Wastewater Management

• Implement rural wastewater management in large number of selected villages

• Each village is unique due to size, topography, etc.

• Applying a program-based approach:

Pilot 10 VillagesExtrapolation,

Complete Framework

Rolling Program Implementation

Until $40 Million is

Exhausted

Rural Wastewater Management• Technology options:

– Individual septic tanks, or

– Piped sewer systems and central treatment

• Participatory process:– At least 80% of households must agree

– Consultation process of technology options

– Responsibility for O&M

• Education, Information Dissemination and Assistance– Encourage behavioral changes

Operating Criteria Structure

• Tiered System Based on:

– Project location (Inside or outside of water supply protection zone)

– Density of community

– Wastewater flow

• Other criteria:

– Treatment systems do not require as much separation to groundwater (0.6 mts compared to 1 to 1. 5 mts)

– Use different soil application rates dependant on the type of treatment system

Project Design Issues

– New field so technical training and transfer of technical information critical at this stage

– Given the relatively low value of projects apparently a lack of interest from firm or Dis to complete individual projects – one suggestion is to have designs prepared for a number of villages to increase value and economize for field surveying and engineering

– Establishing clear design criteria of all aspects of the projects appears to be essential for successful design

– Collections systems are primarily retrofit type projects, which are complicated to design in older mountainous regions

– Limited review of existing projects and design approaches – need to evaluate how well existing projects are working –tendency to keep focused on the work ahead and not on the results behind (common problem in the engineering world especially when there is pressure to produce plans)