Different Approaches to Sewage Treatment -- and to the World

Just below one bank of condominiums at the Sugarbush ski resort near Warren, Vermont, you can find three and sometimes four sewage treatment systems being tested side by side. The story unfolding there is about more than the chemistry of sludge -- it is about the mindsets and values with which human beings attack environmental problems. It's about, if you will, the Future Relationship of Human Beings, Technology, and Nature on This Planet.

Sugarbush has spawned condominiums, restaurants, sports centers, and other profitable sewage-producing entities, built essentially on bedrock. They are most heavily populated when temperatures are below zero, days are short, and biological processes work slowly, if at all. This place is the ultimate test site for sewage treatment schemes. Whatever works here will work anywhere.

And just about everything is being tested, because Sugarbush is desperate. Rice Brook, a small trout stream that drains the mountain, is contaminated in winter with ammonia from the Sugarbush leachfield. The state hit the resort with a $50,000 fine and a moratorium on any further sewage hookups. If the problem isn't fixed before next winter, the state could deny the resort a discharge permit, effectively shutting it down.

Sugarbush's current sewage system is a collection of settling lagoons, which flow into a flocculator that adds aluminum to precipitate out phosphate, followed by a chlorinator, followed by a leachfield, which ultimately percolates into Rice Brook. It is a sophisticated system of the traditional, land-intensive, out-of-sight out-of-mind variety. By Vermont's strict standards, it doesn't handle suburban-density housing on a cold mountainside.

The most high-tech alternative Sugarbush has tried is reverse osmosis. In this procedure the sewage is shoved under pressure through a semi-permeable membrane. Water goes through; everything else stays behind. "A terrific procedure -- it blew everything away! I almost drank it," says a technician at the plant. Reverse osmosis is Space Age sewage treatment at Space Age prices. It generates a concentrated "brine" of stuff that doesn't go through the membrane. The company that sells you the system doesn't tell you what to do with the brine. Sugarbush has decided that reverse osmosis is too expensive and too briny.

There are two remaining contenders.

The first is a squat, square, windowless concrete structure with a sign at the entrance reading "DANGER CHLORINE GAS -- turn fan switch on before entering." Hanging on the wall is a chlorine detector guage, a gas mask and a set of instructions "IN CASE OF A CHLORINE EMERGENCY." Inside is a maze of pipes and dials, gas cylinders and reaction chambers. Bags of dry sodium hydroxide are piled up, each one stamped DANGER CAUSTIC. This is a breakpoint chlorine plant.

Across the driveway is an arched, plastic greenhouse. Inside, under a network of walkways, is a greenish pool with air bubbling through it. The pool is sewage, but the place smells good, like a greenhouse, humid and fertile. Pots of geraniums are in bloom, and rafts of willow and eucalyptus float in the pool. At the far end is a lush marsh -- bamboo and cattail, marsh marigold and swamp iris. There is only one warning sign, and it was put up for a joke -- NO DIVING. This is a solar-aquatic plant, built by the Four Elements Corporation of Warren.

In the breakpoint chlorine process the effluent is made alkaline with sodium hydroxide and then blasted with chlorine gas. The chlorine oxidizes ammonia to nitrogen gas, which bubbles off into the atmosphere. Excess chlorine is inactivated with sulfur dioxide to produce sulfate and chloride. Then the whole business is filtered through activated carbon to remove any remaining chlorine.

In case you didn't follow all that chemistry, one of the operators summed it up, "We make some wicked, wicked water here!" Wicked because this plant must handle ammonia levels ten times higher than usual, so the chemicals are at very high concentration. Wicked because the input chemicals are dangerous, and one possible byproduct, chloramine, is a carcinogen. But wicked in its intermediate steps only, if everything works right. At the end of the process 95-99% of the ammonia is removed, and the effluent contains nothing worse than salt and sodium sulfate.

The breakpoint chlorine plant comes from a pipe-and-valve mentality: "what chemicals can we use to get rid of ammonia?" The solar-aquatic plant comes from an ecological mentality: "how does nature handle ammonia?" It sees sewage not as a waste to be gotten rid of but as a resource to be cycled back into life.

Nature handles ammonia by turning it into nutrient. Normal soils and waters are full of bacteria that transform ammonia into nitrate. Nitrate is taken up into plants, the plants are eaten by animals, the animals excrete ammonia again. That's the nitrogen cycle, one of the great natural flows of the planet.

Over at the solar-aquatic plant John Todd of Ocean Arks International of Woods Hole, Massachusetts, the company that's doing the research for the system, is punching holes into a styrofoam sheet. He sticks willow cuttings into the holes and then floats the sheet on the river of sewage. "I've heard that the Chinese do this," he says. "The willows put down roots and draw the nutrients out. Their leaves make animal feed. I'm trying three kinds of willow to see which works best."

As raw sewage enters the greenhouse it flows first through a cylinder of nitrifying bacteria gathered from Vermont ponds. Then into the raceways where algae multiply in the water, taking up nutrients. Freshwater shrimp eat the algae. Bass and trout in aquaculture tanks at the purified end of the system eat the shrimp.

Todd lifts a corner of a styrofoam float. It's covered with snails and transparent globules of snail eggs. "Here are the hard workers of this place. They clean up the sludge. We drained the plant and found almost no sludge on the bottom." The snails are also fed to the fish.

The river of effluent takes five days to wind from one end of the greenhouse to the other. When it reaches the end, it is filtered by the marsh. The plants there have commercial value (watercress) or pretty blooms (marsh marigold) or the ability to take up toxic substances (cattails, bulrushes). The iris roots produce a substance that kills Salmonella bacteria.

John Todd expects the water coming out of the marsh to be as pristine as a mountain stream. He scoops up a beakerful of it. It looks pristine all right. It tests fairly pristine. The plant meets the toughest standards for an advanced treatment system. "Look at these watercress here at the outtake pipe." (They are yellow and shriveled.) "They're starving -- there's no nutrient left in the water. This stuff is pure!"

The operators over at the breakpoint chlorine plant have difficulty controlling it. "We're here 12 hours a day, watching it like a hawk -- it's real operator-intensive." The alkalinity has to be just right, the chemicals have to be in exact relationship to each other. A mistake can produce a chemical excursion; hence the gas masks and warning signs.

The greenhouse is not operator-intensive, but organism-intensive. With such a variety of species there are many biological pathways, some of which work on sunny days, some on cloudy, some when it's hot, some when it's cold -- as in nature. The worst imaginable mistake might kill off some pathways, but it wouldn't require an evacuation.

"I'm amazed at how resilient these creatures are," says Todd. "Even when they're poisoned, they bounce back." Every other morning at 4 AM the hot tubs in the sports center are flushed with bromine, and a wave of death flows through the greenhouse, but the populations re-establish themselves. A worse poisoning happened last winter, when aluminum from the flocculation system was accidentally routed into the greenhouse inflow pipe. The aluminum tied up phosphate and many organisms "went on hold." Th