(NBBJ) - Vintners in Napa County and elsewhere in the North Bay have found it less expensive to haul high-strength wastewater to the East Bay for recycling, but Napa treatment officials are again asking if there is a better, closer alternative.

Napa Sanitation District, which treats sewage from homes and businesses in the city and surrounding unincorporated areas, has been getting requests from wineries to consider taking in this waste, according to General Manager Tim Healy.

“As more and more wineries are moving in to the south county area, there is more interest in coming up with a solution other than pretreatment on their own or trucking it somewhere else,” Mr. Healy said.

That somewhere else is primarily East Bay Municipal Utility District’s treatment facility in Oakland. On Jan. 27, Napa Sanitation officials plan to gauge whether demand is worth the cost, estimated in a new study to range from the same cost as hauling to Oakland up to 58 percent more, according to a report presented at the Nov. 9 district board meeting.

Less-expensive options for disposing of winery wastewater have been something south county producers have been pursuing since Napa Sanitation started its industrial discharge permit program three decades ago. Discharge permits for Stag’s Leap Wine Cellars and Vinoce were recommended for district board approval Monday, leaving the district to work with seven long-standing wineries without discharge permits, Mr. Healy said.

And district staff studied winery demand for local high-strength disposal in 2009, ahead of completing a master plan for the treatment plant.

The lower end of the projected cost premium over East Bay MUD might be worth considering for Safe Harbor Wine Storage, according to Joel Green, general manager and winemaker. It is located near the Soscol Ferry Road plant and works with up to 3.5 million gallons of wine for clients.

“Everyone would be happy to get trucks off the road,” he said.

East Bay MUD received 1,705 truckloads of winery waste, or six to seven a day, totaling 11.3 million gallons a year and almost 43,000 a day from operations in Napa for the year ending in August, according a Napa Sanitation study.

Napa Sanitation’s total permitted capacity in dry months is 15.4 million gallons a day.

The 7-year-old bulk-storage facility, which added a second building a year ago, forks its process wastewater stream into what’s sewer-bound, with little grape, wine and other vinification leftovers, and what will be trucked to East Bay MUD. A deciding factor of what goes one way versus the other does is the rates Napa Sanitation charges for the strength of the wastewater, Mr. Green said.

Key metrics utilities use for measuring sewage strength, which points to treatment methods needed, are biological oxygen demand (BOD), total suspended solids (TSS) and acidity (pH). For example, BOD in residential sewage averages 175 milligrams per liter, but winery process wastewater averages 7,000.

This medium-strength waste is too much to send through the whole treatment plant and less than the BOD of 20,000 milligrams per liter needed to directly feed wine waste into the plant’s digester, which metabolizes waste in the water into natural gas. Direct injection of waste would take up remaining capacity in the plant and challenge new developments, such as hotels and housing, Mr. Healy said.

A new digester, the most expensive of the six options the district is considering, could cost $15 million. Pretreatment of waste to feed to existing plant treatment ponds, the cheapest option, could cost $3.2 million.

Custom winery Bin to Bottle built its facility in south Napa in 2005 to pretreat its process wastewater to lower its strength then put it into the sewer under an industrial discharge permit. The pretreatment system has been adapted over time to work with permitted discharge capacity of 325,000 gallons a year. Once a year, less than 5,000 gallons of sludge at the bottom of its tanks is hauled to East Bay MUD at a cost of $1,300–$1,400.

“As much as I think it is a good thing for Napa Sanitation to do, it does not matter much for us, because our system is built to not need to wastewater to be trucked as a solution,” said John Wilkinson, Bin to Bottle developer and managing partner.