Turning sludge into `gold'. Simple, low-tech answer to pressing problems of waste disposal can even be profitable

THE front-end loader bites deeply into a towering pile of earthlike material and a cloud of steam billows into the air. It is midmorning and already a soupy humidity has begun to settle over the landscape. The additional steam and heat can only aggravate matters, but Bill Farrel, manager of the Broward County Streets and Highways Division tree nursery, delights in it all. That steam and the rapidly darkening color of the newly turned material tell him all he wants to know: Another batch of the region's wastes is well on its way to becoming a rich compost, or ``black gold,'' as some call it.

Almost every day, trucks piled high with wood chips from local tree-trimming roll up to the five-acre field alongside the county tree nursery. Then come the tank trucks, disgorging a black liquid mud - treated sewage sludge from the nearby towns of Hollywood and Margate.

Six months later, the two problem wastes - one expensive to dump because of its bulk, the other a threat to the aquifer if put in a landfill - have been converted into a beneficial soil conditioner-fertilizer that helps grow a mantle of green.

What isn't used by the tree nursery or sold to landscapers and nurserymen boosts lawn growth along county highways, in parks, and on sports fields. It has made grass grow vigorously on school playgrounds where none survived before. It nourishes stands of sea oats that in turn help keep beach dunes from eroding. It also makes a profit for the county to the tune of about $10,000 a year.

In Maine, Gary Howard and John Hart compost sludge with fly ash from a nearby wood-burning operation at the city's sewage treatment plant. They can't make enough compost to meet the demand.

Stan Bulpitt, a Darien, Conn., nurseryman who began composting fall leaves in Scarsdale, N.Y., long before anyone else saw the need, is still working full tilt. A decade ago, he had trouble finding markets for the compost; now he sits back and watches the orders come in. ``Everything that is composted one year is used up before the [fall] season rolls around the next year,'' he says.

Steadily across the United States, composting operations of various degrees of sophistication are coming on line. They range from shoe-string outfits, such as Mr. Farrel's (a front-end loader comprises the entire ``plant''), to sophisticated, all-mechanized plants.

A 1986 survey by BioCycle magazine showed that 178 municipalities are either operating, constructing, designing, or planning such composting plants - nearly double the number in 1983.

Sludges - the moist wastes of sewage treatment, food processing, and the pharmaceutical industry - along with animal manures, plant debris, and other agricultural wastes, are becoming a major disposal problem worldwide.

Incinerating them is costly and threatens air quality; dumping them is likely to pollute ground water. Before the city of Hollywood began sending its sludge to be composted, it was disposing of the treated waste in a conventional storage lagoon. That lagoon was later found to be contaminating the aquifer. Today, it is on a federal list of toxic waste sites that urgently need to be cleaned up.

Increasingly, composting is seen as the most effective, economical, and environmentally acceptable way to treat these wastes. It does this by converting the highly contaminating raw wastes into a stable humus, one-half to one-quarter of the volume of the original waste. Because the finished compost is so stable, it releases its nutrients at a rate controlled by soil temperature and plant needs. As a result, water-soluble nutrients are never in excess. A heavily manured field may pollute a nearby river, while a heavily composted field will not.

But composting, both in the US and Europe, does have problems. City governments tend to favor costly, high-tech composting plants over the simpler process. Though composting on a large scale has a relatively short history, it has already shown that more highly engineered composting plants are more likely to run into operating problems.

At the Broward County Streets and Highways Division, the composting operation uses the basic ``windrow'' system, in which the ingredients are mixed and piled in long rows, 10 feet wide and 12 feet high. Each row is turned three times during the composting period. Farrel devotes half his time to composting. He has one full-time assistant, who runs the front-end loader.

A front-end loader is virtually the only piece of equipment used to turn out high-quality compost at the Scarborough, Maine, sewage treatment plant as well, and it is the principal piece used by Mr. Bulpitt at Scarsdale.

Ironically, almost alongside Farrel's operation at Pompano Beach, a new, high-tech facility is under construction. On completion, the Fort Lauderdale facility will have cost more than $24 million to build and will require a large labor force to run, yet it will process only one more ton of sludge than the six dry tons a day Farrel's operation handles right now. And that is not all: The new plant is designed along the lines of one in Cape May, N.J., that has been problem plagued.

Six months ago, the Cape May plant was shut down by a fire, thought to have been caused by spontaneous combustion in the compost. It has not yet come back on line. Because composting generates heat, ``we have to assume [fires] will happen,'' says Peter Robinson, consulting engineer on the Fort Lauderdale project.

``We have never had a [spontaneous combustion] fire in our windrows,'' says Farrel of his modest plant. The Scarsdale leaf-composting operation can make the same claim. So can the staff at the Scarborough sewage treatment plant.