Judith Sims. Utah State University.

Transcription

1 On-Site Wastewater Treatment A Sustainable Option Judith Sims Utah Water Research Laboratory Utah State University Logan, Utah jlsims@engineering.usu.edu

2 How Do We Treat Wastewater? Two types of treatment facilities used in U.S. Centralized Decentralized On-site Cluster All types treat wastewater by: Separating solids (primary treatment) Biologically degrading remaining organic materials (secondary treatment) Some systems may incorporate additional tertiary treatment processes to remove nutrients Disinfection may be necessary to eliminate pathogens, depending on receiver system

3 Features of Centralized Systems Large point source of discharge to surface waters Transfer of water away from point of generation May even be transferred from one watershed to another Centralized funding & professional management FAMILY HANDYMAN Magazine, Home Service Publication, Inc., an affiliate of Reader s Digest Association, Inc., Suite 950, Minneapolis, MN 55425

4 Features of Centralized Systems Usually more inviting to growth Typically an all-or-nothing system for area served Economics dictate that everyone within reasonable proximity hook up to sewer Prone to infiltration/inflow problems that intensify with time Requires rehab projects Over-sizing of treatment systems to accommodate storm surges or bypassing of poorly treated wastewater during wet weather

5 How Do We Treat Wastewater? Decentralized treatment t t system (on-site system) Serves an individual residence or commercial facility or a group of residences or commercial facilities (cluster systems) Decentralized - no collection sewers or a single treatment plant for an entire service area

6 How Do We Treat Wastewater? On-site - wastewater is treated near where it is generated Also known as septic systems, or The Beast in the Backyard Associated with low density communities and developments such as rural residences and small commercial facilities Generally consist of a septic tank and a subsurface gravity or y p g y pressurized dispersal system but can include other components such as secondary treatment units and drip dispersal systems

7 On-Site Systems Conventional Gravity Flow Septic Tank-Drain Field Advanced Systems Example: Recirculating Sand Filter

8 How Do We Treat Wastewater? Cluster on-site systems Can serve a small to large number of connections (two to hundreds of structures; most common 5 to 100) Smaller cluster systems serving a few structures resemble onsite systems Larger cluster systems serving hundreds of structures tend to resemble centralized systems Cluster systems generally disperse wastewater t into subsurface dispersal systems Surface discharge or wastewater beneficial reuse (irrigation) may also be used

9 Decentralized System: A Cluster System

10 Septic Tank What About the Solids? University of Minnesota Cooperative Extension Service Tank must be pumped periodically to remove solids - referred to as septage

11 What Do We Mean by Treatment in a Soil- Based On-Site System? Soil treatment processes Physical filtration ti and entrapment t of contaminants t in soil pores Chemical precipitation of contaminants (for example, phosphorus) Chemical adsorption of contaminants to soil particles (especially to clay minerals) Nitrate, the cause of blue baby syndrome, does not significantly adsorb to soil particles Biological decomposition of organic contaminants Organic contaminants and pathogens serve as lunch for native soil microorganisms i Pathogens also die-off if retained in the soil long enough

12 What Do We Measure to Assess Wastewater Treatment? Organic materials BOD 5 - Biochemical oxygen demand - amount of oxygen used in the breakdown of organic matter Is an indirect measurement of the organic content of a water sample Pathogens Indicator organisms - Fecal coliforms/e. coli (bacteria whose presence indicates that the water may be contaminated with human or animal wastes)

13 What Do We Measure to Assess Wastewater Treatment? Nutrients Phosphorus Nitrogen forms NH 4+, NO 3-, Organic nitrogen Total Nitrogen is all of the forms Total Kjeldahl Nitrogen measures ammonium and organic nitrogen

14 Nitrogen Nitrogen, in the form of nitrate, t is also of human health concern Nitrate levels in drinking water above regulated levels (10 mg/l (ppm)) may be toxic when consumed by infants less than 6 months old Blue Baby Syndrome Also implicated in other health problems

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16 Case Study: On-Site Treatment Through 4 ft. of Fine Sand EPA/625/R-00/008 Parameter (Units) Septic Tank Effluent Soil Water at 0.6 m Soil Water at 1.2 m BOD (mg/l) 93.5 <1 <1 TKN (mg/l) NO 3 N (mg/l) Total P (mg/l) E. coli (Log # per 100 ml) Non-detect Non-detect

17 How Do We Treat Wastewater When Site Conditions are Limiting? In places where difficult site conditions i prevent the use of septic tank/drain fields, some jurisdictions allow the use of advanced (usually more complex - often called alternative) systems Also sometimes used to provide a higher level of Also sometimes used to provide a higher level of treatment than can be obtained with conventional system

18 How Do We Treat Wastewater? Limiting Conditions Difficult conditions that may prevent use of conventional system Small lot sizes High ground water Shallow depth to bedrock High permeability soils with excessive amounts of gravel, rocks, or sand Low permeability soils with large amounts of clays Proximity to water sources May need higher levels of contaminant removal for pathogens and nutrients, especially nitrogen

19 Benefits of On-Site Systems If properly planned, sited, designed, d installed, lld operated and maintained, on-site systems can provide level of treatment necessary to protect public health and meet water quality standards F ll ii ih l l i For small communities with low population densities, often are most cost effective option

20 Benefits of On-Site Systems Avoid transfer of water from one watershed to another Recharge local aquifers through subsurface disposal, maintaining the groundwater supply and a base flow for surface waters Other water reuse opportunities include irrigation close to point of wastewater generation Use of drip irrigation is becoming more common

21 Challenges of On-Site Systems Many older systems in use today do not provide adequate treatment, resulting in adverse effects on public health and the environment and negative effects on property values Were installed as temporary systems, assuming centralized system would replace them Were installed in unsuitable sites and locations More than half of existing systems are over 30 years old At least 10% of these older systems cause wastewater to back up into the home or surface in the yard Many local health departments do not have records of many of these old systems

22 Management Programs In many small towns and rural areas, where houses are spaced widely apart, septic systems may be the most practical & least expensive way to treat household wastewater However, few communities i have developed d organizational structures for management of on-site wastewater systems Though such programs required for centralized wastewater facilities and for other services (e.g., electric, telephone, water, etc.) to provide professional management

23 Management Programs To protect ground and surface waters, an on-site system should be managed throughout the life of that system to ensure that the system performs satisfactorily over its service life When homeowners are responsible for managing their systems, inadequate operation and lack of routine maintenance often leads to system failures, with a resulting perception that on-site systems are not reliable Given a choice, people would just rather flush and forget about what they put down the drain

24 Management is a Good Idea Implementation of a management program can control the effectiveness of wastewater treatment to protect public health and the environment Management programs can take on many forms and vary in level of responsibility assumed by the program and by the system owners A management program is especially important when alternative systems are used Alternative systems are usually more complex than the conventional septic tank/soil absorption system and require more frequent and specialized maintenance

25 Goals of an On-Site Management Program Rd Reduce risks ik to public health by: Wastewater backup into homes or onto soil surfaces Prevent groundwater and well contamination Minimize risks from public contact with system components Minimize i i risks from inadequate disposal of septage

26 Goals of an On-Site Management Program Prevent and reduce effects on water resources, including nutrient over-enrichment and pathogen and contaminant discharges Protect sensitive aquatic habitat and life Abate public nuisances by eliminating odors Abate public nuisances by eliminating odors from systems or from transportation and disposal of septage

27 Approaches to Achieve On-Site Management Program Goals Local Health Districts may: Administer a permitting program for on-site systems Manage or oversee on-going monitoring and maintenance of systems Implement corrective action programs for failing systems Provide or require certification and licensure for on-site system professionals Facilitate appeals and variances Comply with UIC (underground injection control) and storm water programs Offer inspections of on-site systems during real estate transactions Develop a public education and outreach program

28 The Utah On-Site Training Program Utah Administrative Rule R Persons who design, inspect, and maintain underground disposal systems, and who conduct percolation tests or soil evaluations for these systems, must be certified by the State of Utah The Utah On-site Wastewater Treatment Training Center at Utah State University i has been designated d as the provider of training as well as the administrator of examinations for certification of those persons who design, inspect, maintain, or conduct soil and percolation tests for underground wastewater disposal systems

29 MOU for Decentralized Wastewater Treatment In 2005 EPA developed a Program Strategy for the Decentralized Wastewater Program identifying EPA s vision, mission and actions to improve performance of onsite wastewater treatment systems One of the components of the Program Strategy is a Memorandum of Understanding di (MOU) between EPA and fourteen organizations involved in managing decentralized wastewater systems. Including Ground Water Protection Council and NOWRA MOU is intended to: Upgrade the professionalism within the industry, leading towards efforts to improve system performance, promote education, expand knowledge levels, and increase communication concerning onsite issues

30 Resources National Onsite Wastewater Recycling Association NOWRA.org U.S. EPA Onsite Program cfpub.epa.gov/owm/septic/septic.cfm?page_id=260 Consortium of Institutes for Decentralized Wastewater Treatment MOU Partners