From BioCycle Magazine
September 2000, Page 29

BIOSOLIDS IN HONOLULU
COCOMPOSTING AT PEARL HARBOR
Following stricter landfill disposal regulations for biosolids, the U.S. Navy looked for a less expensive alternative. Composting became the Navy’s answer, and the solution is also helping the city/county of Honolulu.

When the Hawaii Department of Health tightened its restrictions on landfilling biosolids by requiring the lining of sludge drying beds, the U.S. Navy Public Works Center (PWC) at Pearl Harbor decided to look for a less expensive alternative to landfilling. Biosolids composting became the Navy’s answer. A pilot project was started in July, 1997, and the full-scale program became operational in 1999.

The composting facility at the PWC receives biosolids from the Navy’s wastewater treatment facility (WWTF) at Fort Kamehameha and the Army’s Schofield WWTF, as well as the City and County of Honolulu’s Honouliuli WWTF. Green materials are collected from the Navy’s tree trimming and ground maintenance contractors. The city and county also provide yard trimmings to the facility as part of its agreement with the Navy. The facility has a design capacity of treating 15,600 wet tons of biosolids annually.

Located in an old coral pit, the site has a 300 foot by 300 foot lined pad for aeration and processing. The pad was constructed with a coral surface working layer on top of a more impermeable clay barrier. There are approximately 15 acres of curing and compost storage area. Biosolids from the Navy and Army WWTFs are handled separately from the Honolulu material, since the finished compost from the Navy and Army is permitted for application on federal Department of Defense (DOD) lands, while the city/county feedstocks are used for landscaping public areas.

Yard trimmings chipped prior to delivery at the site are mixed at an approximate ratio of three parts green material to one part biosolids. (The actual ratio is determined by the operator based upon moisture levels and other factors.) Combined materials are placed in a ten-foot-high static pile on top of air supply lines, where they remain for about three weeks. After trommel screening, chips larger than a half-inch go back into an aerated pile, while the screened compost is transferred to a curing windrow where it is watered and turned for three to four months. Temperatures and moisture content are monitored regularly to ensure pathogen and vector reduction. Leachate is collected and used to provide added moisture to windrows and aerated static piles.

PETROLEUM HYDROCARBON LEVELS

“One unique local characteristic (and treatment difficulty) we encountered in our composting program,” says Stan Konno, PWC environmental department director head, “is the high level of diesel range total petroleum hydrocarbon (TPH) content in the sludge from the WWTF at Fort Kamehameha.” Oil from past leaks in pipelines and tanks — which go back to 1941 — penetrates the wastewater collection piping system and causes the high hydrocarbon content. “We were asked to develop a process to degrade the TPH contaminants as well as convert the biosolids into compost,” explains Dennis Chang, the solid waste branch manager and site operator.

Contamination levels in the biosolids can be as high as 200,000 ppm (about 20 percent contamination of the biosolids). Resultant analyses confirmed that the finished compost exhibited no detectable toxicity, leading the Hawaii Department of Health to allow unrestricted use of the end product on DOD property. To illustrate that the compost produced would have no ill effects on either plants or the environment, PWC — in cooperation with the Navy Facility Engineering Service Center (NFESC) at Port Hueneme, California — conducted a field study (“Assessing the Fate and Impact of Residual Hydrocarbon-Like Components in Composted Biosolids Applied to Garden Soil”). A test plot (20 by 20 by 3 feet) was divided into four sections. Composts of different ages (20 days, six weeks and 11 weeks of curing) were applied to three sections; the fourth section served as the control. Carrots and onions were planted for evaluation. Studies of plant viability and yield showed that there was no significant difference between plants in the test plots versus the control. Hydrocarbons were not detected in any of the pore water samples using two different EPA methods.

TIPPING FEES

Tipping fees for biosolids delivered to the PWC compost site are comparable to charges at the local landfill, notes Konno. “For city and county deliveries, we charge $72/wet ton, with a ‘surcharge’ of $10/ton for the compost since it gets applied on public projects,” he points out. For the military, there’s currently no extra charge beyond the $72.

Looking ahead to expanding organics recovery on Oahu and other Hawaiian islands, the PWC staff points out that “we’re using almost all the biosolids being generated on the Department of Defense side on Oahu. It’s up to the county to send us additional quantities of biosolids.” The Navy and Army are each sending nine wet tons/day (five days/week) of biosolids to the composting site. The city/county of Honolulu is delivering twice a week, providing a total of 40 wet tons a week. On February 1, 2000, PWC Pearl Harbor was issued a five-year operating permit from the Hawaii Department of Health. The permit provides that compost produced from the military’s wastewater biosolids is not restricted in its use and application provided it remains on DOD property. It also notes that capacity may be increased up to 200 wet tons/week of biosolids from the city and county of Honolulu.

The Navy’s biosolids facility was named Project of the Year by the American Public Works Association Hawaii Chapter for the less than $2 million category. “We’re very proud of our facility and the personnel who manage it,” said Konno. “This award serves to recognize their accomplishments and confirm the Navy’s commitment to protect Hawaii’s fragile environment.” — J.G.