Oneida Lake: ever-changing ecosystem

Managing water resources in Oneida Lake, WM Kappel

Oneida Lake watershed: A valuable diverse ecosystem, SM Harrington

Water level management, HM Goebel

Oneida Lake: undergoing ecological change, EL Mills, KT Holeck

Evolution of the Oneida Lake fishery, T VanDeValk, L Rudstam

Regional partnerships for Oneida Lake watershed, AB Saltman

Helping to protect Oneida Lake, J Henke

Trends: technology and management of municipal wastewater, D Interdonato, E McCarthy

Outstanding young researchers

President's message, D. Ellis

Executive director's message, P Cerro-Reehil

People and places

Joint CSO/SSO meeting

Correction

Winter 2001 — Vol. 31, No. 4

by David Interdonato and Eileen McCarthy

New approaches promise better wastewater treatment with lower costs.

In the 1960s and 1970s, the goal of sanitary wastewater engineers was to provide sewage treatment to densely populated areas. Wastewater treatment is now widespread, and different challenges face wastewater operators and designers. Cutting-edge technology is allowing these challenges to be addressed with an emphasis on quality treatment and cost-effective management.

Today, some sewerage providers, especially in densely settled or rapidly developing areas, are capping the amount of additional wastewater they will accept and adding to the list of restricted contaminants because of a lack of funds and space constraints on capital upgrades. In some states, the regulatory climate points to a trend away from large treatment plant expansions. As a consequence, utilities do not want more or cannot accept more wastewater or wastewater with higher treatment needs.

Also, as growth is reaching its limits in some urban and suburban areas, development is occurring in rural locations without sewage infrastructure. In these locations the drinking water source is usually limited to ground water, small lakes, and streams. To protect the quality and quantity of the ground water supply, state regulators may restrict its use to drinking water and effluent discharge forcing developers to seek ways to conserve and reuse the water.

These challenges create new demands that innovative technology and management techniques can address. With a need for tertiary treatment and indirect water reuse, small community wastewater treatment systems, such as those that employ membrane technology, are becoming workable solutions to a growth-limiting problem. In addition to advances in treatment technology—based on new guidelines for constructed wetlands—bio-uptake of wastewater is an environment-friendly alternative to traditional treatment methods.

Other technological advancements in disinfection, such as ultraviolet treatment, are allowing municipalities to meet stricter regulations in a safe and effective manner. Improved technologies can treat biosolids efficiently to meet land-spreading regulations that restrict the amount of contaminants that may remain in the biomass. Energy conservation has increasingly taken on a creative application by using gas produced by biological activity (for example digester gas and methane) to create energy and partially to power plants.

Technology

Small community systems

Residential, commercial, and even industrial development is moving beyond the suburbs, but the infrastructure for water or wastewater treatment is not keeping pace. Well water is used for potable water in isolated developments, but for multifamily complexes and shopping centers, septic systems are not acceptable for wastewater treatment. Small community systems with tertiary treatment are becoming popular in such locations. As an added benefit, they return treated water to the aquifer.

New treatment technologies for low-flow include fixed-film package treatment systems, geotextile filtration, and membrane filtration. Other methods include drip irrigation, evapotranspiration systems, and mound systems. These systems are now being fine-tuned for unique problems encountered with small-scale flows.

The major benefit of these new systems is that the higher quality effluent can be discharged to ground water for indirect reuse. Because of low flows, the size of these systems is small; they are generally easy to operate, and they are inexpensive. Beyond small community developments, they can also be used as temporary infrastructure at military camps, large construction sites, disaster relief operations, concerts, festivals, and seasonal camps.

Micrograph of Giardia's locomotion machinery

Membranes

Chemical and biological processes can eliminate most pollutants and pathogens in municipal wastewater. Physical processes, such as separation and rejection, are imperative for removing small particulate contaminants including Cryptosporidium, Giardia lamblia, viruses, pesticides, metal ions, and other dissolved solids. Membranes can perform this physical removal. Membrane filter systems vary by pore size (the smallest particle that can pass through).
 

Category	Pore size	Description
Microfiltration	0.1-10 µ	Removes particulate matter and is the most common method of municipal filtration
Ultrafiltration	0.01 µ	Generally remove pathogens and separate biomass from treated effluent (more commonly used in drinking water systems)
Nanofiltration	0.001 µ	Remove pesticides and herbicides (from, say, CSO and other source of infiltration)
Reverse osmosis*	0.0001 µ	For water reuse applications, frequently used to remove ionic species and salt from solution and all dissolved constituents

*Highest level of treatment.

Because of the level of secondary treatment currently required, membrane filtration has become an increasingly popular solution for small systems and small municipalities. Membrane microfiltration is replacing secondary clarification because it gives wastewater plants the ability to operate with poor settling sludge, smaller space requirements, higher efficiency, and ease of operation; these benefits result because the method requires no process adjustments or controls as are needed with clarifiers. Moreover, it is cost-effective to use filtration over traditional treatment on small-scale applications.

In many cases, separate developments such as assisted-living complexes and residential complexes are turning to a potent and economical combination of biological treatment and microfiltration for their wastewater needs. These combined systems are gaining increased popularity and acceptance from regulators because of their treatment capabilities,and from private developers because of their reduced capital and O&M costs.
 

Zenon "packaged plant": high-efficiency activated-sludge system combined with fully automated secondary microfiltration membrane unit.

Reuse

Tertiary treatment, such as membrane filtration, is not only valuable for protecting human health, but it also provides a new opportunity for industry to limit water use and wastewater production. The catalysts for these reuse projects include the scarcity of ground water and the generation of high-salt and high-BOD wastewater that local utilities may not accept.

New reverse-osmosis filtration systems, sequencing batch reactors and cloth filter systems, clarifier-continuous backwash systems, and DAF-filter systems (dissolved air filtration) are solutions for water recycling in industrial plants. Because of the outstanding performance of these new technologies, water use in some of plants has decreased by as much as 90%, and wastewater generation has been eliminated.

Constructed wetlands: tertiary treatment

Wetlands

In the past, constructed wetlands were only used for tertiary treatment of small volumes of water. With publication of the USEPA manual, “Constructed Wetlands Treatment of Municipal Wastewaters” (Fall 2000), small communities' use of wetlands as their basic wastewater treatment has been made acceptable. With sufficient land area, wetlands can provide adequate passive treatment. Aerobic and anaerobic conditions of these systems with microorganisms and with vegetation and gravel filters provide the majority of treatment.
 
Wetland treatment: Pros and cons

Pro	Con
-Requires minimal skilled labor -Natural appearance and ecological benefits -Little energy required.	-Large area needed for complete treatment -Lack of data on cost-effective construction and operation.

UV treatment

Final disinfection is a constant hurdle among operators and designers because of the need to balance costs and treatment effectiveness. Chlorine is the traditional form of disinfection because of its relative low costs and competence, but it is a “super biotoxin” and creates problems with chemical handling, storage, and organic interactions forming chlorine-produced oxidants. It is well known that when chlorine and organic matter have significant time for interaction, chloroform, bromodichloromethane, and other trihalomethane compounds can form.

UV technology disinfects by radiating microorganisms to prevent their replicating and requires only a short contact time. Chlorine and other chemical disinfectants, on the other hand, cause chemical reactions within microorganisms and require a contact time of up to 180 times that of UV light. Pulsed UV light systems are on the forefront of wastewater technology because they destroy pathogens more effectively and at a higher rate than traditional disinfection and standard UV light.

Since the early 1940s, guidelines for UV disinfection have been available. The high cost of UV treatment and the lack of a residual following application had made it unpopular for potable water disinfection; however, these concerns are not as relevant in wastewater treatment.

UV treatment is becoming an economical alternative because it can diminish costs for power, labor, parts, chemicals, and overall O&M. Moreover, advances in lamp and ballast design, cleaning mechanisms, and power modulation have led to a decrease in costs over the past few years.

Biosolids

Engineers have few options for disposal of biosolids. Land-spreading and incineration have been the standard methods of disposal, but new restrictions on reuse of biosolids reuse are making land-spreading less desirable. To address these restrictions, biosolids require more thorough treatment to decrease the levels of nitrates, fecal coliform, and pathogenic bacteria.

Temperature-phased anaerobic digestion (TPAD) is a new technology that can improve the quality of biosolids by combining thermophilic and mesophilic anaerobic digestion. TPAD consumes biosolids more rapidly than other methods, produces more methane (which can become usable energy), creates less biosolids mass, and destroys most coliform and pathogenic bacteria usually found in municipal biosolids. The treatment plant in Independence, Iowa uses TPAD to produce Class A biosolids that have a low pathogenic organism content. The product can be applied on land in public access areas.

SCADA control system component

Control systems

Energy is the largest and most variable cost for a wastewater treatment plant. Instrumentation and controls can address energy scarcity. Control systems, such as programmable Logic Controllers (PLCs) and SCADA systems, can help to conserve energy with variable-frequency drives; energy-efficient motors; heating, cooling, and ventilation improvements; lighting modifications; and fuel cells. Load management strategies, demand strategies, and cogeneration are also feasible energy conservation techniques.

Management

Asset management systems

Over the past 50 years, spending on infrastructure in the U.S. has focused on construction with little regard for the cost of necessary O&M. Today, sewage infrastructure and wastewater treatment plants are aging and deteriorating without a ready source of funding for improvement.

Regulations and standards of practice are now being implemented for infrastructure management, accounting, and financing to prevent this problem from escalating. In 2000, the Governmental Accounting Standards Board introduced Statement 34 (GASB 34), a governmental accounting process that requires municipalities to account for their fixed (infrastructure) assets. Unlike accounting practices in the past, municipalities must either depreciate their wastewater infrastructure assets or use an asset management program to support maintenance and preservation of their capital.

For GASB 34 to be effective, an asset management program is necessary to plan for and fund O&M and capital improvements. Such a program is needed to budget for maintenance, determine asset reliability, and develop a capital replacement schedule. By focusing on the critical assets of a municipality, a team of engineers, operators, and accountants can integrate their knowledge to increase a wastewater facility's life.

Engineers will be able to provide the expertise to determine the current value and condition of infrastructure as well as the best schedule for maintaining these assets. By using broad system planning, engineering models can be developed to determine tradeoffs for maintenance, rehabilitation, and replacement for aging infrastructure. This important management technique will allow better planning for O&M rather than rebuilding infrastructure.

Revenue generation

Revenue generating practices are becoming popular for treatment plants with excess capacity. An appropriate time to determine excess capacity is when a municipality is analyzing methods to extend the life of a treatment plant through asset management.

Because the incremental cost of treating additional sewage is small, treatment plants can sell their excess capacity to small communities and industry both to treat primary influent or dispose of biosolids. Another method of revenue generation, credit trading for effluent, is currently under discussion and will be designed after the successful air emissions trading program. This incentive program will give well-performing wastewater treatment plants an opportunity to benefit financially from their quality effluent. Such an arrangement, though not yet near implementation, can motivate municipal managers to maintain and improve their treatment abilities.

SSOs and CMOM

Throughout the nation and especially in the urban Northeast, sanitary sewer overflow (SSO) and combined sewer overflow (CSO) lead to unregulated discharges. The Wet Weather Water Quality Act of 2000 addressed these problems through the Capacity, Management, Operations and Maintenance Program (CMOM). CMOM aims to help local sewage authorities develop a site-specific plan of capital improvements and maintenance for their collection systems. It encourages the development of a management plan to outline steps to mitigate SSOs and CSOs.

A variety of grants and potential aid are available to help institute a CMOM program. The money can be used to intercept, transport, control, or treat municipal CSOs and SSOs. The Urban Wet Weather Priorities Act is a federal grant program to fund urban wet weather initiatives including overflows. The goals of the CMOM initiative fall within these two grant categories.

 

Municipal wastewater treatment technology and management are evolving with a variety of advances in both areas. As regulations and approaches to wastewater change, new methods for dealing with water quality must be promoted. New technology in the areas of small community treatment, membrane filtration, UV radiation, constructed wetlands, and control systems will enhance the ability of water quality professionals to address their treatment issues. Reuse, asset management, final biosolid treatment, revenue generation and CMOM will allow wastewater treatment plant operators to address new regulations and increase their efficiency.
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David Interdonato is a senior project engineer in the wastewater department of Schoor DePalma, a New Jersey-based engineering and design firm. Phone 732-577-9000. Eileen McCarthy was an intern at Schoor DePalma. She is in her senior year in the Management & Technology Program at the University of Pennsylvania.