Renewable Energy

SYSTEMS AND POLICIES

ANAEROBIC DIGESTION FACILITIES - - - - - -

IN SWITZERLAND With a long history of promoting self-

energy and food production, Switzerland now has seven facilities which anaerobical l y digest source separated household organics.

Maria Kelleher

HILE most people associ- ate Switzerland with stun- ning scenery, great cheese and watches, few link the country with leading edge waste processing technolo- W m. ~ u t in auiet. efficient

Swiss style, the cGntry has a u i b e r of op- erational anaerobic digestion (AD) plants generating natural gas and electricity from organic residuals.

Waste management in Switzerland dif- fers significantly from other countries in Eu- rope and in North America. Switzerland has a rigorous policy which requires 95 percent of all waste sent to a landfill to be "stabi- lized," a policy that ensures that very little organics decomposition takes place in the landfill itself.

There are very few landfills in Switzer- land. The country has 40 incinerators (this number will be reduced to 28 in the future), and incineration is the disposal option for most waste in the country.

The waste management cost structure for incineration and organic waste processing in Switzerland is somewhat different than North America. A tipping fee of 150 Swiss francslmetric ton (mt) ($98.55 USImt) is charged at the AD facility, which compares to 200-250 SFImt ($131.40 to 164.25 USIton) charged for incineration. Because Swiss mu- nicipalities cannot send their waste directly to landfill if it contains any unstabilized or-

ganic material, Swiss municipal solid waste (MSW) tends to be in- cinerated. Some mu- nicipalities are willing to implement source

The Otelfingen anaerobic digestion facilitv near Zurich proceises 13,000 mt/year of source separated organics, mainly yard trimmings and food residuals.

separated collection of organics in order to sen8the-orgpiic portion of the waste stream to the less expensive AD plants for process- ing. There is a mandatory requirement for local electrical utilities to purchase all ener- gy generated by anaerobic digestion plants a t 0.15 SF (9.8 cents US)/kwh, which pro- vides a healthy revenue source to these anaerobic digestion plants.

Switzerland has seven anaerobic diges- tion facilities which process a total of 71,000 mtlyear of source separated organic (SSO) household waste. Two of these plants (Aar- berg and Villeneuve) use Dranco technology. A Valorga plant with a capacity of 10,000 mtlyear of source separated organics was constructed near Geneva in 2000. Kom- pogas, a Swiss company, has four plants in the Zurich area, with a combined capacity to process 40,000 mtlyear of SSO.

Kompogas is a Swiss company, an offshoot of a well established construction operation, which about ten years ago developed an anaerobic digestion technology. Kompogas has 16 AD plants in Europe (four in Switzer- land, six in Germany and six elsewhere), and one pilot plant in Japan. The list in- cludes four plants which they own and oper- ate themselves near the Zurich airport.

To date, the company has invested 30 mil- lion Swiss francs in the business. They ini- tially spent ten million SF to construct their early plants, which can now be constructed in a shorter time for about half of that amount. The cost savings have been achieved through a more modular and pre- fabricated approach, and building the di- gesters outdoors, to avoid the need for ex- plosion proof buildings and fixtures.

The Kompogas technology has recently been certified in Japan, a process which took over two years. Kompogas has a licensing arrangement with a local agent in Japan, and one pilot plant in Kyoto.

THE KOMPOGAS OTELFINGEN PLANT The Otelfingen Kompogas plant was con-

structed in 1997. Located near the Zurich airport, the plant processes about 13,000

mWyear of source separated organic waste, Many different plants are consisting of 70 percent SSO from a popu- grown in the a uaculture lation of 100,000 in small cities and vil- greenhouse OteIBngen lages near the plant and 30 percent com- ~~~~~~~~~ mercial waste (e.g. from farmers who make salads for McDonalds, etc). About 70 per- cent to 80 percent of the household residu- als are yard trimmings and 20 percent food residuals.

The plant requires about 5,000 sq. meters for its total footprint. It is located in an in- dustrial area with an office building as a neighbor, and has no odor complaints. Three people work at the plant five dayslweek, eight hourslday. During weekends, one per- son looks after the four Kompogas plants in the-area.-There is an alarm system-which alerts the operator to any problems at a spe- cific plant.

- - -- Incoming waste-is shredded, then sorted - -

to remove contaminants such as plastic and glass. A magnetic separator is used to re- cover any ferrous metal material ahead of the digester

Residuals go to a second shredder, then to an intermediate bunker, which is used as a storage unit for mixing and regulating the flow to the digester. The shredded materials stay in this intermediate storage tank for two days. Water from the dewatering unit is added to SSO in the storage unit, to adjust the feedstock moisture content to 28 percent dry solids content, 72 percent moisture con- tent. A piston pump delivers the shredded

waste to the digester, which is a concrete tank with a capacity of 1,000 cubic meters. A heat exchanger heats the residuals from 25°C to 55°C.

The Kompogas technology uses a plug flow digester with a 15 to 20 days retention time. The digested waste is dewatered with a screw press to 50 percent solids content. After two days, the solid digestate is sent to

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The new digester at Volketswil (above) was prefabricated -

from steel with a thin aluminum coating and provides sufficient heat for the- di estion process even during cogd Swiss winters. The windrow cornposting (far right) site next to the Volketswil digester has a capacity of 15,000 mt/year.

farmersJ fields for land application. Kom- pogas pays the transportation costs to the land application sites, and does not receive any revenue for the material. The Kom- T~gasdigestate quality is usually at half the current limits for heavy metals. Nickel is usually closer to the limit. There is a suspi- cion that grass close to roadways may accu- mulate trace amounts of nickel from tires, but this has not been proven to date.

Some of the water from the dewatering process goes back to the plant. Farmers use the remainder as fertilizer (the N and P con- tent is of value).

Two engines (180 kW and 110 kW) gener- ate power on site. Twenty-five percent of the energy is required for in-plant needs; 75 per- cent is surplus energy which is sold. Kom- pogas cleans the gas on-site and uses it as a

fuel in their fleet of cars and trucks. The gas cleaning process is proprietary; and the com- pany has invested heavily in perfecting it.

The rough rule of thumb on gas produc- tion-is 100 cu.m of gaslmt of waste input, and up to 150 cu.m/mt if pure food waste is processed. The biogas is typically 60 percent methane, therefore each mt of waste can produce six kwh of power.

The Kompogas car and truck fleet can all operate on natural gas or gasoline as a fuel source. The economics of fuel conversion make it worthwhile in Switzerland because of supportive government policies. The costs vary for different car and truck manufac- turers. I t costs about 6,000 SF more for a dual fuel engine in a Mercedes car; the Swiss government refunds 50 percent of this cost. The gas produced by the anaerobic digestion ~ l a n t is about 60 ~ e r c e n t of gasoline cost

1 56 ~ e r c e n t by Korn~o~as , and 50 ~ercen t by theswiss g&ernmLni. ~ o c a l schools get in- volved in doing research at the greenhouses. For instance, science students at the local school figured out the aeration rate required for water hyacinths, water lilies and plants used as fish food.

Kompogas is considering establishing a small farm with animals such as rabbits who would feed on the plants from the greenhouses.

NEWLY CONSTRUCTED DIGESTER AT VOLKETSWIL The anaerobic digester at Volketswil was

constructed in 2001 and applies current state-of-the-art technology in Kompogas plant design. The digester for the facility was prefabricated from steel with a thin aluminum coating. It was moved to the site in one piece, which is a challenge with a 25m long reactor with a 4m diameter. The tank was moved to the site a t night to min- imize disruption of traffic. The outside in- stallation is viable in a cold climate. There is enough heat available to keep the di- gester a t the right temperature, even in a cold winter (temperatures in Switzerland can be minus 20°C in winter). The mixing

and storage units are the core of the diges- tion process and these continue to be locat- ed within a building.

The Volketswil plant is a t an open windrow composting site, which developed an odor problem. The local government required the owners to put in anaerobic digestion to pro- cess the waste with the highest oxygen de- mand, to get the odor problem under control. The site now anaerobically digests about 5,000 mtlyear, and maintains outdoor windrow composting capacity of 15,000 mvyear. There is sufficient space available to add a second digester, if required. On-site curing can be carried out in the open windrow composting area as there is lots of space.

The tip fee a t the open windrow site was - 128 SFImt, but has been raised to 148 SFImt to cover the additional costs of the

I anaerobic digestion facility. An estimated 2.5 million SF was spent on equipment and buildings to provide anaerobic digestion for 5,000 mtlyear

THE DRANCO DIGESTER IN AARBERG There are two Dranco plants in Switzer-

land: Aarbere (11.000 mt) and Villeneuve - . , (8,000 mt). Aarberg is located in the French part of Switzerland in the Bienne-Biel dis- trict, which has a population of about 130,000. Input to the site is mostly source separated household organic materials.

At Aarberg, there was an existing open windrow composting site which experienced odor problems. The Bienne-Biel district pro- duced 20,000 mtlyr of wet fraction. They built a digester that handles 11,000 mtfyr, and the remainder is processed in the open windrow composting operation.

Incoming waste is crushed to 40 mm man- imum size, followed by a magnetic separa- tor. It is then sent to a dosing unit (inter- mediate hopper). A heavy duty piston pump, which is also used by the concrete industry, is used to load material into the digester.

Incoming material is heated to 55"C, using steam exhaust from the motor. Dranco feels that steam injection is a more efficient method of heat exchange and provides better process and temperature control, and they prefer this to adding hot water to the feed- stock. A small amount of the steam condens- es, which adds to the moisture content in the reactor. The energy content of the steam is about 2,700 kJlkg. By comparison, the ener- gy content of water at 990~-is 420 kJ/kg. The Dranco process is thermophilic (occurs at a temperature higher than 55°C) - essential for disinfection and destruction of pathogens.

At the Aarberg plant, seven parts of recy- cled material are mixed with two parts of fresh material and one part steam (to provide the necessary heat). The incoming feedstock is loaded into the reactor at three points at the top of the reactor for plug flow. Recircu- lation provides the mixing required in the di- gester. Dranco estimates that all of the reac- tor contents are recirculated in three days.

D R Y I N G S Y S T E A

- The digested material is at a solids content of 18 percent to 35 percent in the digester.

Stringent landfill The Dranco process operates a t as high a solids content as ~ossible, but at no higher

all electricity generated by the digestion site, as it is classified as renewable energy.

LESSONS FROM SWITZERLAND

policies in than 40 percent solids content. The dewa- tering press increases the solids content of

Switzerland ensure the digestate from 20 to 25 percent solids to

Switzerland has a population of seven mil- lion, and has seven digesters which process source separated organic waste from house- holds. If prorated to the U.S. and Canada, we would have over 300 digesters in North America, but we have only three in Canada and a few in the U.S. Even though interest is growing substantially, the numbers are like- ly to grow much more slowly than in Europe.

The Swiss government has a long history of promoting self-sufficiency in all aspects of life, including energy and food production.

Many-ofits policies are designed to develop renewable energy sources, and broaden the number of different energy sources used in the country. Their stringent landfill policies are designed to ensure separate processing of organic residuals.

High incineration costs combined with few other options lead to an environment where anaerobic digestion facility opera- tors are assured a high revenue for energy sales. This "hedging your bets" strategy on energy sources promotes an integrated ap- proach to waste management, which makes sense for all kinds of reasons, envi- ronmental and other. rn

48 percent to 50 percent solids. Water from separate ~rocess in~ the 1.2 mm filter Dress is metreated in an RBC (rotating bidogical contactor) on-site residua'w before discharging by sewer to the Lyss WPCP (water pollution control plant).

A gas motorat the site generates electric- ity. Steam from the gas motors is used to heat incoming material. There is a gas stor- age unit with a capacity of 380 cum. on site. Excess gas is flared if the motor is-down~Gas production ranges from 80 up to 150-170 cu rn/mt; average about 100-110 cu mlmt. The carbon content of the waste is 30 percent to 35 percent. It has a low organic content (65 percent), and a moisture content of 37.5 per- cent average.

The same trucks which deliver the waste to the site take back the digestate to the aerobic facility for two to three weeks of curing. The aerobic compost is used by farmers at no cost.

The construction business next to the Aar- berg Dranco site purchases heat from the fa- cility. The possibility of using steam to heat concrete elements to speed up curing and eliminate need for some chemicals has been considered but not explored in detail to date. Dranco is paid 15 Swiss centskwh by law for

Maria Kelleher is Director of Resource Efficien- cy at Enviros RIS, based in Toronto, Canada.

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