CHAPTER 14 – Water Reuse

WATER REUSE

• Reuse of wastewater involves direct application of

treated wastewater for:

– Agricultural & urban irrigation

– Industrial reuses, groundwater recharge

– Street cleaning, car washing, and toilet flushing

• Reuse applications require treatment ranging from

secondary treatment to advanced tertiary treatment

• A decision to develop reuse is often economic

– A result of viewing wastewater from a disposal

perspective or as a water resource

14–1 WATER QUALITY AND REGULATIONS

• The U.S. Environmental Protection Agency does

not govern water reuse permitting or regulations

• Regulations for many reuse applications have been

adopted by individual states

– No state has regulations that include all potential

applications

• Combining treatment & water-quality requirements

produces reclaimed water of acceptable quality

– Reducing the number of criteria to be monitored

14–1 WATER QUALITY AND REGULATIONS

• Types of reuse may be grouped into categories of:

– Restricted and unrestricted agricultural irrigation

– Restricted and unrestricted urban irrigation

– Industrial reuse, and groundwater aquifer recharge

• Many states require testing/certification of new

processes/equipment

– To establish limits on loading and identify subsequent

treatment requirements

• Some states apply letter grades (A through C) to

recycled water quality

14–1 WATER QUALITY AND REGULATIONS

• Nutrient removal during treatment is not required to

meet water-quality reuse requirements for any state

– But has some advantages in water-quality issues

• Salinity increases as water is reused for potable and

agricultural purposes and results in salt buildup in

soils and water supplies

– A concern to semi-arid & arid areas using recycled water

• Engineering reports serve as a preliminary design

reports

– Required by most states to obtain recycled water permits

14–2 AGRICULTURAL IRRIGATION

• Agricultural reuse is advantageous:

– Treatment requirements are often moderate

– Wastewater contains plant nutrients and soil amendments

– Agricultural areas may be adjacent to treatment plants

– Income is gained by growing cash crops

• The supply of wastewater is continuous, but demand

for irrigation water depend various conditions

– Storage is needed to balance irrigation supply/demand

14–2 AGRICULTURAL IRRIGATION

• Loading rates are determined by hydraulic, organic,

nutrient, and salinity limits

• Background groundwater quality, crop type, and

irrigation method are required to help set maximum

loading rates

Restricted Agricultural Irrigation

• Reuse water for irrigation of fodder, fiber, and seed

crops presents the least opportunity of human contact

– Allowing less stringent treatment requirements

• Treatment & water-quality requirements vary by state

– From lagoon treatment to secondary treatment with

disinfection

• Storage is based on a minimum detention time or

water balance requirements

– Some states require longer storage for additional

treatment and pathogen removal

Unrestricted Agricultural Irrigation

• Unrestricted irrigation of crops includes processed

food crops and foods eaten raw

– Required water quality depends on application method

• Spray irrigation requires a higher degree of

wastewater reclamation than surface irrigation

• Required water quality varies with above-ground

and root crops, and fruit formation on trees

• Buffer zones are provided between domestic water

supplies and adjoining property based on use

Unrestricted Agricultural Irrigation

• Results of secondary treatment by chemical addition,

coagulation, filtration & long-detention chlorination:

– 2.2/100 ml fecal coliform and turbidity below 2 NTU

for foods eaten raw

– Fecal coliform limits in the range of 23 to 1000/100 ml

for processed food

• Storage required for detention ranges from 5 to 15

days or is based on rainfall and loading rates

14–3 URBAN IRRIGATION AND REUSE

• Urban irrigation includes golf courses, landscaped

medians, parks, and front & back yards in some areas

• Water degraded during storage may require additional

treatment for algae removal

– And chlorination to maintain a residual

• Piping systems are identified by color-coded pipe

– Cross-connection is prohibited, and other connections

restricted

Restricted Urban Irrigation

• Where transient human activities occur, vegetation

should be allowed to dry

– Excess water should be allowed to soak into the ground

• Additional treatment may be required for removal of

solids that can plug nozzles

– And chlorination to prevent growth in the irrigation system

• Storage is based on detention time or water balance,

and loading rates are typically less than 2.5 in./week

– But depend on vegetation and weather conditions

Unrestricted Urban Irrigation and Reuse

• Unrestricted irrigation includes parks, playgrounds,

schoolyards, residences, and commercial landscaping

– Also toilet flushing, fire protection, and construction

• Unrestricted reuse water must be pathogen free

– Requiring a high degree of treatment and disinfection

• Some states require secondary treatment/disinfection

– With storage lagoon detention of 15 to 150 days

14–4 GRAY WATER AND INDUSTRIAL REUSE

• Residential gray water is wastewater from clothes

washers, bathtub, shower, or sink

– Separate from toilet, dishwasher & kitchen sink

• Industrial gray water is manufacturing process waste-

water that may or may not require treatment for reuse

– Within the manufacturing facility, or irrigation/landscaping

• Gray water use is typically not considered a reuse

– It is part of industry water conservation program

14–5 CONSTRUCTION AND OTHER

REUSE APPLICATIONS

• The largest water reuse for construction is dust control

– Others include soil compaction, irrigation & cement mixing

– Flushing of toilets and urinals for office high-rises

• Treatment requirements vary with the method of

application and potential contact by the public

14–6 GROUNDWATER RECHARGE AND POTABLE

SUPPLY

• Groundwater recharge may result from surface

infiltration or direct injection

• Discharge to surface waters used for potable water

supplies is continues to be addressed by many states

14–6 GROUNDWATER RECHARGE AND POTABLE

SUPPLY

• Rapid infiltration operates on a fill-and-drain basis

– Water is added to a depth of 3 to 5 ft (1 to 2 m) and

left to percolate into the ground

• The degree of treatment depends on:

– Type of application to the soil

– Soil formation and chemistry

– Depth to groundwater and dilution available

– Residence time to the point of extraction

• Proper operation includes drying, rest time & disking

– Reduces clogging by surface straining of bacteria & algae

14–6 GROUNDWATER RECHARGE AND POTABLE

SUPPLY

• Direct injection to groundwater with TDS levels < 3000

mg/l must meet/exceed drinking water standards

– With the highest degree of wastewater treatment

• Drinking water quality requires:

– Biological, chemical, and physical processes to reclaim

the water and remove pathogens/organic compounds

– Removal of inorganic salts to reduce the total dissolved

solids concentration, reducing salinity

14–6 GROUNDWATER RECHARGE AND POTABLE

SUPPLY

• Total organic carbon (TOC) measures gross amount

of carbon from organic sources

– Includes natural and synthetic organic compounds

• Total organic halide (TOX) and TOC are used as a

measure for removal of organic compounds

• Augmentation of a drinking water supply includes:

– Direct injection of reclaimed water into the drinking

water aquifer

– Discharge to surface water impoundment with limited

dilution

14–6 GROUNDWATER RECHARGE

AND POTABLE SUPPLY

Direct potable reuse is the immediate

distribution of reclaimed water into the

potable water distribution system

Direct potable reuse is not

practiced in the United States

14–7 DESIGN OF IRRIGATION SYSTEMS

• The initial step in design is to define characteristics of

the wastewater effluent quality, and site conditions

– The iterative process (Fig. 14–2)

• Regulatory limits on effluent quality are established to

protect groundwater, surface water & public exposure

14–6 GROUNDWATER RECHARGE

AND POTABLE SUPPLY

The iterative procedure for determining field

area for irrigation involves interdependence of

hydraulic loading rate, nitrogen loading rate,

water storage volume & crop selection

System monitoring, the method of water

distribution, discharge control, and agricultural

management are final considerations

14–7 DESIGN OF IRRIGATION SYSTEMS

The water balance is calculated

by the relationship:

The nitrogen balance is calculated

by the relationship:

14–7 DESIGN OF IRRIGATION SYSTEMS

• Water storage is required due to imbalances between

the reclaimed water supply and the application rate

– Determined by crop growth and climatic conditions

• Irrigated vegetation takes nutrients from wastewater,

maintains soil permeability, and reduces soil erosion

• Crop selection is determined by the reclaimed water

quality, required nitrogen uptake, and profitability

• Design of recycled water distribution systems require:

– Coordination of supply, demand, water storage, and

distribution system piping and pumping

14–8 DESIGN OF URBAN DISTRIBUTION SYSTEMS

Design of recycled water distribution

systems requires coordination between

supply and demand, water storage, and

distribution system piping and pumping.

Coordination of Supply and Demand

• Demand-side management includes limiting demand

– Optional demand applications where recycled water

can be used as available

• Supply-side management includes supplemental

sources of supply

– Groundwater, surface water, or potable water

• All recycled water systems must be designed with

provisions for both disposal of excess water and

supplemental supplies for periods of supply shortfall

Storage

• Wastewater, the source of recycled water, varies in

quantity from day to day and from month to month

• Daily storage scattered throughout the distribution

system is used to equalize daily supply and demand,

• Storage in ponds or reservoirs may be combined with

decorative, recreational, or water resource uses

• Aquifer storage may be limited to groundwaters that

cannot be used for public water supplies

Storage

• Recycled water storage is classified based on the

degree of treatment and exposure to the public

– A landscape impoundment is for recycled water storage

– Restricted recreational impoundment is for storage

where boating and fishing is an intended use

• Non-body-contact water recreational activities

– Nonrestricted recreational impoundments are for

storage in which no limitations are imposed on body-

contact or water recreational activities

Distribution System Design

• Distribution of recycled water is similar to potable

water distribution

• Recycled waterlines must be 3 ft. away from

(horizontal), or 18 in. below potable waterlines

• Distribution systems are analyzed for pipe size,

pressure, velocity, and variations in demand

– Using a computer modeling software such as EPA NET

Distribution System Design

• Design of treatment/distribution systems must allow

provide the highest possible degree of treatment

– Under varying circumstances

• Large storage reservoirs may adversely affect

recycled water quality due of algae growth

– And nutrient peaks caused by seasonal turnover

• Algae and other solids increase system maintenance

by clogging small orifices, nozzles, and drip emitters

– Growth may be controlled by nutrient removal during

treatment or by chlorination and filtration at the reservoir

Pressure

• Recycled water systems tend to be pressurized by

continuous pumping

– Operating pressures tend to be higher than for potable

water distribution systems

• Standard design pressure range is 50 to 100 psi

– System pressures may be up to 150 psi

Cross-Connections

• Raw water and treated potable water may be used

as backup for the recycled water supply

• Potable water supplies must be protected by isolating

and protecting cross-connections between recycled

and potable water

• Connected systems will contaminate a potable water

system if the potable system is at a lower pressure

– Backflow protection must be used to prevent

contamination of a potable water supply

Agricultural Irrigation at Tallahassee, Florida

• The application of wastewater effluent to agricultural

land has been done in Tallahassee since 1966

• A 16-acre agricultural farm was established as an

alternative to additional treatment for nutrient removal

– To avoid pollution of a downstream lake

• The farm expanded over 20 years to over 2000 acres,

with a capacity of 23 mgd (Figs. 14–3 & 14–4)

Frontyard and Backyard Residential Irrigation at El

Dorado Hills, California

• El Dorado Irrigation District in California provides

potable water & operates 2 recycled water plants

– And a dual-plumbed residential distribution system

• The recycled water systems are connected and

operate under a single Master Reclamation Permit

(Fig. 14–6)

• A 66-mg reservoir & pumping system disposes of

recycled water at a golf course and a local lumber mill

• The district approved the concept of upgrading in

1990 to meet unrestricted urban reuse requirements

Urban Reuse at St. Petersburg, Florida

• St. Petersburg is the largest U.S. city to achieve

complete reuse with a goal of zero discharge

• To avoid the cost of nutrient removal & offset irrigation

demands, the city upgraded its wastewater treatment

plants to allow unrestricted urban irrigation (Fig. 14–7)

• When irrigation is not available, excess recycled water

is injected into a deep-well saltwater aquifer

– Reject water that does not meet reuse standards is also

injected for disposal—zero discharge to surface waters

Industrial Reuse for Power Generation

• Delta Diablo Wastewater Treatment plant provides

recycled water to the Los Medanos Energy Center

– Design capacity is 16.5 mgd with excess treated effluent

discharged via deep water outfall

• Power plant uses are feedwater for the heat-recovery

steam generator makeup & evaporative cooling water

• Treatment facilities consist of:

– Screening; grit removal; primary clarification

– Tower trickling filters; activated sludge

– Secondary clarification; disinfection and dechlorination

Water Reclamation for Groundwater

Recharge and Injection

• California’s OCWD is responsible for a large ground-

water basin providing Orange County’s drinking water

• Recharge basins were located in Anaheim & Orange

on the Santa Ana River

– To enhance percolation of surface water into the ground

• Due to overdraft from irrigation and well water for

potable uses, saltwater had encroached as far as

five miles inland

Water Reclamation for Groundwater

Recharge and Injection

• In 1976, the agency commissioned Water Factory 21

to reclaim wastewater for injection into groundwater

– To replenish groundwater for 75% of the residents

– Build a hydraulic mound to protect inland areas from

seawater intrusion

• WF 21 was replaced with a new facility that expanded

the existing seawater intrusion barrier (Fig. 14–9)

– Distribution includes a pipeline to groundwater recharge

basins in Anaheim, and expansion of the recharge basins

Water and Wastewater

Technology

Seventh Edition

Mark J Hammer

Mark J Hammer, Jr

CHAPTER END