October 26, 2010 | General

Composting Biosolids Into High Quality Agricultural Product (Israel)

Screening compost in IsraelBioCycle October 2010, Vol. 51, No. 10, p. 39
Compost Or processes 20,000 metric tons/month of biosolids with shredded municipal green waste in an extremely hot and arid climate.
Dan Sullivan

DANIEL Ungar began on a path to what he considers his “life project” 25 years ago as a mechanical engineer designing agricultural machinery. Now, as CEO of Compost Or Ltd. in Tel Aviv, Israel, he is helping tackle one of his country’s most pressing challenges – dealing with human and other organic wastes in an environmentally responsible and cost-efficient manner.
“The government asked me to find solutions for sludge,” he recalls. “Twelve years ago we were allowed to spread it in our fields – not for vegetables but for animal [feed] corn and wheat. Since 2007, we are not allowed to do that. Now you must produce Class A sludge [per Israel standards]. Before it was Class B. The simplest way to handle it is to make compost.”
An extremely hot and arid climate combined with an underwhelming amount of green waste for amendment present some challenges. “We get green waste from cities – all kinds of Mediterranean and subtropical trees like palm, poinciana, cypress, pine and other ornamental trees,” says Ungar. “They shred it for us. Their other option is to send it to the landfill. They prefer to give it to us; it’s much cheaper for them. We get about five to seven trucks every day -18 wheelers that hold 70 to 80 cubic meters each.” Compost Or Ltd. processes that green waste with about 40 percent of Israel’s treated biosolids – about 20,000 metric tons per month – into a high-grade product for agricultural application.
“We are screening into a very fine material of about 10 millimeters,” says Ungar. Green waste that doesn’t pass through the screen gets recomposted with the fresh green waste in equal amounts. “We recycle green waste again and again into the windrows so we don’t have anything to send to landfill,” he explains. “It’s good starter because it is very warm material and the digested sludge is very cold.” It’s also very wet, Ungar adds, between 16 and 22 percent solids.
Ambient temperatures that soar up to 50°C (122°F) present challenges not only for the biological environment but also for the heavy equipment used to manage the process. Ungar says he runs every piece of machinery for a maximum of three years before replacing it. “We have two drum screens, two big wheel loaders – a Volvo L-150 and an L-120 – and two windrow turners and that’s it,” he says. The company is waiting for delivery of a compost turner from SCARAB modified to take the heat and meet other challenges of managing such a high volume of material.
Ideal compost windrow size for biosolids, Israel
“Daniel had never operated a SCARAB when he came to us for help in addressing three main problems,” says Mike Winter of SCARAB Manufacturing in White Deer, Texas. “There is so much material on his site that windrows are not just placed shoulder-to-shoulder but are several feet deep where the windrow edges meet. Pushing this material aside as windrows were turned proved to be too much for the smaller torque hubs on his turners.” (Ungar says he has already replaced three hubs this year.)
Besides installing torque hubs on the track-drive SCARAB three times larger than the ones on Ungar’s previous machines, specially designed track clearers will allow the turner to move through the slick material in windrows without losing traction. An oversized radiator substantially exceeding the engine manufacturer’s specifications will allow for smooth running at extreme temperatures. And the drum will be belt driven, Winter says, thus reducing fuel consumption by about a third. “We need a strong machine and a simple machine with a good cooling system – that’s it,” says Ungar.
After much experimentation, Ungar has found the best size windrow to be 5 meters wide by about 2 meters high. “I’ve tried many size windrows – bigger and smaller – and each has its advantages and problems,” he explains. “With wet sludge, if you build too high, the windrow collapses after two days and then it’s 6 or 7 meters wide and very hard to turn. Also, if it’s too big air cannot go inside, so the [composting] process is very long. A big windrow can be an advantage if you are in a rainy area – otherwise it becomes wet and the process stops. Our area is dry and so we find that 5 meters wide and 2 meters high is the best solution.” Newly formed windrows are mixed for the first time after three days and then every six or seven days. “After 30 to 35 days it’s ready – then we leave the compost on a big heap for two to three weeks for ripening and then supply it to the farmer,” Ungar says.
He adds that heavy metals are not an issue because of Israel’s tough standards with regard to treating wastewater and keeping industrial wastewater out of the municipal wastewater stream. Compost Or processes about 15,000 metric tons of biosolids and about 5,000 metric tons of green waste/month, yielding about 7,000 to 8,000 cubic meters of finished compost for agricultural application at a rate of about 24-32 m3/acre. “We’re getting really good quality compost,” says Ungar, adding that negative perceptions over the use of biosolids in agriculture are virtually nonexistent. “All the agricultural advisors from the government are helping me to sell the materials. There is much more demand than we can produce. I could sell three times more than I have.”
Compost Or monitors windrow temperatures every two days; at the end of the process, a bucket of finished compost is sent to the lab to check for macro and micronutrients, percentage of organic matter and to make sure the media is free of pathogens and any other harmful contaminants. “I have an agreement with the government that I must send them test results confirming that there are not any pathogens in the windrows at the end of the process,” explains Ungar.
He is about to take organics recycling in Israel to the next level by collecting commercial and residential food waste, digesting it to produce biogas and composting the digestate. “We are going to collect organic home waste and make biogas out of it,” he says, explaining that the feedstock will be stored in hermetic rooms to be mined for biogas before being composted in large concrete containers. Ungar plans to invest $25 million into what he considers his crowning achievement, and expects the government to support up to 50 percent of infrastructure costs once the economics make sense. “Right now the tax to put waste in the landfill is not high enough,” he says. “But in two years time I believe that the government is going to begin charging three times more. It’s going to be $30 to $40 per metric ton. Then it will be much cheaper to bring material here than to send it to the landfill.”
In the meantime, there is still much to be accomplished with regard to managing human waste. “Fifty percent of it is still going to the sea – it’s a very serious problem we’ve been fighting for many years without much success,” Ungar says. “The problem is with Tel Aviv, the biggest city in Israel, and its suburbs. Other cities are making sludge and we are taking it and making compost.”
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