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Alternatives to the big pipe.

This article does not have a happy ending. It describes a problem that affects most of the pocketbooks of greater Boston. The problem's history is not unique to Boston, nor is its technical solution. Chosen after decades of angst, a secondary wastewater treatment system and a long pipe to convey treated effluent out of Boston Harbor are now under construction, following a slow, legally and technically convoluted, unimaginative, environmentally and financially unreal process. For there to have been a happy ending, the process would have brought each community to bear responsibility for wastewater treatment, water conservation programs, sewer-pipe maintenance, sludge composting, and effluent discharge, and affordable rates would have enabled the communities to carry out all these responsibilities effectively.

The Massachusetts Water Resource Authority (MWRA) wastewater system is a gigantic spider web of pipes that conveys sewage through a treatment plant and currently discharges it into Boston Harbor. As suburban Boston has grown over the past 50 years, towns elected to extend the city sewer pipes rather than build their own wastewater treatment plants. This was a low-cost choice for those taxpayers, but it carried a high cost for the environment (Boston Harbor is one of the most degraded harbors in the US) and for current taxpayers, who must now make up for 50 years of negligence, as Paul Levy describes beginning on page 53.

Our society seems afflicted with a malaise that makes us incapable of dealing appropriately with sewage: Piping it away is the only solution we've come up with. As the volume of wastewater has grown, our solutions have been either a bigger pipe or a longer pipe, or both. The result is that now Boston has the Big Pipe when we might instead have had the Little Pipe, the Clean Water Pipe, or No Pipe.

Going With the Flow: the Little Pipe

We are taught early in life that sewage carries disease, smells bad, and is not a fit topic for polite conversation. Sewage is water contaminated with waste--feces, urine, food scraps, grease, soap, blood, soil, paper, small toys, solvents, metals, cleaners, hair--from houses, businesses, and industries. Most Americans who have overcome their inhibitions and contemplated the subject have focused on the "waste" rather than the "water" component of wastewater. Actually, both components should be minimized.

In the two decades since passage of the Clean Water Act, the US has invested billions of dollars installing and repairing pipes and pumping stations to convey sewage to and from wastewater treatment plants. This activity has moved a lot of water and a relatively small amount of waste from one place to another. Despite the combined efforts of the US Environmental Protection Agency (EPA), state environmental agencies, academics, and civil engineers to improve collection and treatment technologies, most municipal systems are still hydraulically driven to compensate for low flow, peak flow, average flow, and design flow (what the flow will be 20 years from now).

Where does all this flow come from? Some of it is water added to the waste at the source to enable the material to flow. A lot of it is water that gets into the system because the collection pipes leak. The rest of the water, at least in our older cities, comes thundering into the system through pipes that convey storm water through the sewage treatment plant. Allowing rainwater into a sewage treatment plant is illogical and ultimately counterproductive, but the aged systems of Boston, New Bedford, Providence, Chicago, New York, and countless other cities cannot prevent this from happening unless they are redesigned and rebuilt. This is why Boston is constructing a new Big Pipe.

Reducing Wastewater at the Source

Source reduction has a wide range of benefits, including water conservation and cost reduction. Most people are aware that potable water is not an unlimited resource and that individual efforts are needed to reduce the demand for drinking water. Conservation also has indirect economic benefits, as it reduces or even removes the need for new reservoirs or wells, water treatment, and distribution systems. Massachusetts has state regulations intended to reduce water use. For example, low-flow appliances are required in all new construction, and citizens are urged to change bad habits by turning off the water while brushing their teeth or washing their cars with a bucket of water instead of a running hose.

In areas where sewer and water bills are based upon gallons actually used, residents can more clearly see the benefits of conservation: less usage = lower costs. Higher water rates and water-conserving appliances can reduce per capita use from 80 to less than 50 gallons per day, with little change in life style. In a city of 500,00 people, that alone would reduce flow to the sewage treatment plant by 15,000,000 gallons per day.

MWRA user fees are assessed per hookup to the water system rather than per gallon used or discharged. Flat fees are less costly to administer, and help to rationalize long-term financial planning. Flat fees also incorporate the fact that while flow may be reduced through a variety of techniques, the waste being carried by the water--the "loading" or "the solids"--remains the same per capita.

There are ways to reduce the loading of every gallon of water entering the MWRA system. For example, it is technically possible to provide tertiary quality septage treatment for all of the homes and businesses in the MWRA network that still rely upon septic tanks for wastewater treatment. Most septage is collected by private haulers (honey wagons) who dispose of the foul, highly concentrated waste material in designated manholes in the sewer system. Since every 1,000 gallons of septage equals about 30,000 gallons of sewage, removing 100,000 gallons of septage every day would reduce the daily load of solids at the Deer Island plant by 3,000,000 gallons. Instead of being added to the Deer Island load, septage could be delivered to one of several dedicated septage treatment plants strung like pearls along route 128. Another way to reduce the load is to ban garbage disposals. These common kitchen appliances add grease and organic loading; prohibiting their use could reduce the volume of solids or sludge by as much as 5 percent.

While conservation technologies can reduce flow, and local septage treatment and banning garbage disposals can decrease loading, one way to reduce both is to remove some towns from the MWRA system. Big towns such as Natick, Framingham, and Walpole could build tertiary treatment systems using any of a range of technologies (including sequencing batch reactors, Solar Aquatics, or rotating biological contactors) at a lower cost per taxpayer than staying in the MWRA system. This would reduce the load on Deer Island's secondary treatment plant and the flow out the pipe into Massachusetts Bay.

Capital and operating-cost savings from reducing loading into the MWRA system are likely to be substantial. A proportional reduction in waste loading by removing septage and ground garbage would not only reduce capital costs, but also lower solids (sludge) handling costs. Nearby Cape Cod Bay would benefit as well, since with reduced loading, there would be fewer nutrients entering the bay via the pipe.

Reducing the Volume of Wastewater from Infiltration

People are frequently surprised to discover that most sewage pipes leak in the opposite direction to what they fear. They leak in. The infiltration of groundwater into gravity sewers both dilutes the waste and increases the flow to the sewage treatment plant by anywhere from 10 to more than 100 percent, depending upon the age and location of the pipes. Furthermore, most people have been willing to pay for more pipe rather than less, to get the wastewater as far away as possible. Unfortunately, more pipe means more infiltration, which means increased flow to the treatment plant. Given these facts, we pay a high price for our desire to transport the problem rather than solve it.

There are established technologies for installing and maintaining small-diameter pressure sewers, small-diameter gravity sewers, and vacuum systems that are generally less expensive and have no infiltration problem. The existing MWRA collection system is very leaky and poorly maintained (see Sewer Infrastructure: An Orphan of Our Times, page 53). A program of staged replacement and a well-funded and professionally operated maintenance program for the collection system is needed throughout the MWRA network.

Reducing the Volume of Wastewater from Storm Sewers

Storm water falling on greater Boston has few places to go: Most of the soil is covered with paving or buildings, rivers and creeks are channeled, paved, or piped, and many wetlands have been filled for industrial, commercial, or residential structures while others have been dredged to improve shipping channels. The rain sweeps up contaminants from the roads, sidewalks, and ditches, and then flows downhill, flooding manholes, underpasses, and streets. When the catchment basins are full, the water flows to the sewers, to and through the sewage treatment plant, and out the pipe as if through a giant funnel.

Aside from overloading the treatment facilities, this leaky sewer system makes an excellent storm-water collection system, but it has two flaws: it directs flows to only one p~ace, and that is the wrong place. Storm water should be dispersed, not concentrated. Instead of flowing to the sewage treatment plant, storm water should flow or be pumped to swales, bogs, fens, maple swamps, grassy wetlands, and dells, where it can be filtered and treated by soil, roots, stems, and leaves, and their associated microorganisms before it flows into rivers and ponds and ultimately into Massachusetts Bay.

Swimming Against the Flow: the Clean Water Pipe

Under the Clean Water Act, in effect since 1972, we have been guided to design wastewater collection and treatment for high flows and low loadings. The new Clean Water Act (now up for reauthorization) should motivate us to control the flow, reduce water use, encourage industrial pretreatment and reuse, reduce the extent and improve the quality of piping, and build cost-effective treatment systems that treat waste rather than funnel water.

Traditional wastewater treatment involves solid/liquid separation followed by chlorine disinfection of the liquids. The liquid effluent may be land applied, directly discharged, or piped to a waterway. The solids (sludge) may be composted, burnt as fuel or incinerated, landfilled, land applied, or converted to fertilizer pellets for land application. Until a few years ago, sludge was also dumped at sea.

Considerable progress has been made in the last two decades to improve treatment methods. Modern treatment plants may have multi-stage solid/liquid separation, aeration to reduce the 5-day Biochemical Oxygen Demand or BOD5, sludge digestion, and chlorination followed by dechlorination. (An index of organic loading, BOD5 is a measure of the amount of oxygen that is consumed in five days to degrade the material. Discharge with a high BOD5 "steals" oxygen from fish and other organisms.) Treatment plants usually remove 20 to 30 percent of the nutrients (especially nitrogen and phosphorus) with the solids; tertiary treatment removes most of the remaining nutrients from the liquid portion.

The treatment plant under construction on Deer Island for the MWRA system will discharge cleaner water than the old facility--secondarily treated sewage rather than primarily treated sewage. But to qualify for the Clean Water Pipe option, MWRA must treat the water to tertiary quality. This seems unlikely given:

* repeated insistence by MWRA, EPA, the House, the Senate, and ratepayers that tertiary treatment is not needed,

* legal and financial commitment to a path with no forks or room to turn around, and

* lack of money.

Even if hydraulic loading could be reduced by 50 percent, there would be additional costs to operate the physical plant to meet tertiary standards.

Reversing the Flow: No Pipe

During the 1970s and 1980s, we had a "Sewer America" program to get the wastewater from our cities and towns sufficiently treated to meet Clean Water Act standards. The federal government paid for 90 percent of the design, engineering, pipes, treatment plants, and outfall and discharge pipes for these systems. The standard operating philosophy has been to collect the sewage and pipe it away--far from homes, neighborhoods, and businesses. Large, centralized plants would then "treat" the water to an acceptable limit, disinfect it, and discharge it to a river, lake, or ocean.

There were some benefits from sewering America: Cities with inadequate collection and treatment systems were able to upgrade to adequate systems, and direct discharges of raw waste into lakes, rivers, and oceans stopped. Large systems were built because community leaders assumed they had only one chance to obtain federal dollars for these projects, so they built in 1975 what they might need in 2015. Expensive systems were built because the municipal portion of the cost was less than 10 percent (sometimes less than 5 percent) of the real cost. The outcome of this (combined with many layers of bureaucracy) was that the close attention to costs that one sees, for example, when a small town buys a new ambulance, did not exist. It was easier to apply for one big grant than several small ones, so centralized systems were preferred over small, community-based ones. This was also under the belief that wastewater could be moved great distances without harm to the environment or the economy.

With major dollars under consideration, conservative design was the rule, and true innovation was stifled. Thus technologies developed and proven in the 1940s and 1950s were redesigned in the 1960s and built in the 1970s and 1980s.

Flow volume is too great in the Boston system for "No Pipe" to be a feasible solution, but it is comforting to contemplate reversing some of the flow. With today's technology, attractive and acceptable treatment plants could be designed for neighborhoods, communities, or towns on the outer edges of the MWRA network to handle conservative flows from homes and businesses. These might include industrial pretreatment, sludge recycling, and water reuse, and they could be esthetically integrated into the environment. Piping wastewater away removes the public from the problem-and-solution process, and moving water around costs a lot of money. It would behoove us, then, to keep the water where the people are, instead of expensively sending it into the sea. Local control and the awareness that goes with it would encourage communities to clean and reuse water to recharge aquifers, irrigate fields, and restore ponds and lakes.

Meeting the Nation's Needs for Wastewater Collection and Treatment

Wastewater needs good collection and treatment systems. We need pipes that don't leak and treatment plants that degrade the organic material, remove nutrients, and destroy pathogens without creating chemically contaminated byproducts. We need management systems for sewer pipes, and funding to repair and replace them. And we need to do all this at a price that homeowners, businesses, and industries are willing and able to pay.

Existing wastewater systems are evolutionary dead ends. Bigger is not better. Collection and treatment costs are skyrocketing, technological and financial innovations are slow to enter the marketplace, water reuse remains rare, and water--good, clean, drinkable water--is wasted rather than conserved. Wastewater needs to be treated on a community basis, so that it can be conserved, pretreated to remove contaminants at the source, and then recycled; the resulting liquid can be used for groundwater recharge, the nutrients for growing plants, and the solids for soil amendment (such as fertilizers and bulking agents).

We are at the start of a new administration that is dedicated to rebuilding the economy. As part of economic development, the federal government, including EPA and the Departments of Commerce, Agriculture, and Interior, needs to incorporate a Water Policy such as that suggested by the Water Environment Federation in Water Quality 2000 (available from Water Environment Federation, 601 Wythe Street, Alexandria, Virginia, 22314). Such a policy would involve integration of new technologies, ecological principles, and sound public and private finance. Our nation's water system needs help--not just money thrown at it for public works projects, but help in cleaning and restoring the water in ways that are of long term benefit to society and the environment.

Susan Peterson is an anthropologist (Ph.D., University of Hawaii) and farmer (150 acres of lovely New England soil) whose professional career began in Woods Hole 20 years ago. Following more than a decade in the Marine Policy Center at Woods Hole Oceanographic Institution, she taught at Boston University and then founded Ecological Engineering Associates, a for-profit company that sells Solar Aquatics|TM~ wastewater treatment systems to industry and municipalities.

Treatment Technologies

All wastewater treatment relies upon microorganisms in the wastewater to degrade organic material. The three technologies described below each use a different strategy to maintain the microbial populations (biomass) at peak performance.

Rotating Biological Contactors

Rotating biological contactors are large plates or disks threaded on a central shaft, much like a spindle, partly submerged in wastewater. Microorganisms attach to the surfaces of the disks over time and this biomass rotates through the wastewater, coming in contact alternately with the organic material that the microorganisms degrade and the air where oxygen is adsorbed. Occasionally the biomass slough off the disks and become sludge. Rotating biological contactors are most often used for secondary treatment, although they can be used in series to produce tertiary quality effluent.

Sequencing Batch Reactors

Sequencing batch reactors are "fill and draw" tanks operated as follows: 1) fill the tank with raw sewage, 2) aerate the tank, 3) settle the tank, 4) draw off the liquid portion, and 5) draw off the sludge (settled solids) if necessary. The biomass remains suspended in the sludge, available to degrade the next batch of raw sewage. This technology is typically operated to achieve secondary treatment; it can be modified to produce tertiary quality treatment.

Solar Aquatic Systems

Solar acquatic systems combine aquaculture systems with constructed wetlands. These are flow-through systems, housed in a greenhouse, where the raw sewage is aerated in clear-sided tanks and lagoons planted with a wide range of vegeration. The biomass is maintained on the roots of the plants and in the mixed liquid. Following this step, the partially treated sewage is settled, solids (sludge) are partially recycled and removed, and the liquid portion flows through a constructed wetland. These systems produce tertiary quality wastewater.
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Title Annotation:wastewater disposal
Author:Peterson, Susan
Publication:Oceanus
Date:Mar 22, 1993
Words:3032
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