Topsoil: sugary success you can't beet

In today’s commodities markets, sugar has started to peak as renewed enthusiasm in stock and commodities takes hold. This is good news for British Sugar, whose processing plant at Wissington in Norfolk is dependent for its long-term livelihood on the demand for sugar and in particular, EU sugar quotas.

In October 2008, SCI’s Horticulture Group visited the British Sugar plant. Although the primary horticultural interest lies in the production of topsoil as a by-product of the sugar extraction, there was much else to see and admire. A key to the success of the plant is that none of the by-products of the process are wasted.

The tour was over-subscribed and many missed out on the opportunity to venture through the plant. However, thanks to the generosity of British Sugar, future visits are being arranged.

The Wissington factory is not hard to find. The large silos dominate the surrounding flat Fenland landscape. Fenland soils provide ideal conditions for growing sugar beet, and the adjacent river Wissey provides the water required for processing.

The plant works 24 hours a day. Some of the beet is piled in the yard for processing overnight and over the weekend. The rest goes straight into the processing plant, where it is washed, diced and then passed through large rotating drums where the sugar is dissolved out. Here the process is split, and half the sugar liquor goes into storage to be purified during the spring and summer when no fresh beet is coming in.

An essential part of the liquor purification process is the addition of lime to separate impurities. The lime is later recovered, but while it is no longer pure, it can be used to adjust soil pH, for example, in growing sugar beet, or as part of the casing layer that stimulates the mushroom mycelium to produce the fruiting bodies we eat. Thanks in part to the irregular shape of the beet, five percent of every load delivered to the factory consists of good Fenland soil. This is washed off the beet and the muddy water is diverted to large ponds where the soil can settle out before the clean water returns to the river.

In these ponds, the simple action of gravity pulls the heavy sand particles out of the water close to the inlet, leaving the silt and clay to settle further down the pond – just as a river sorts the sand and mud at its mouth. Thus, when the ponds have been drained and dried out, the three basic soil ingredients of sand, silt and clay can be reclaimed separately. They are then re-mixed in controlled proportions to provide topsoil and subsoil mixes for use in the landscaping and sports industries. Needless to say, soil is not the only waste product. A considerable amount of energy is involved and some inevitably ends up as irrecoverable low-grade heat. This is used to heat Cornerways Nursery situated next to the plant, where 3500 tons of tomatoes are produced each year. Furthermore, it has long been known that tomato yields benefit from elevated CO2 levels in the enclosed atmosphere of a glasshouse. Here again, the CO2 is simply a by-product of combustion in the factory’s CHP plant, fed via 70 miles of pipes directly into the glasshouse atmosphere.

One of the lesser known by-products extracted from sugar beet is betaine (N,N,N-trimethylglycine). In the plant, this acts primarily as an osmolyte, protecting the plant against desiccation without interfering with the action of the plant’s enzyme systems. Betaine has found a number of uses in medicine, although it is primarily an additive to fish food, where it has been shown to promote the growth of farmed fish.

The main product of the factory is white granulated sugar, which goes into industry with, for example, Coca Cola being one of the largest customers. Sugar beet residue becomes animal feed and to provide an outlet for any surplus sugar, an experimental bioethanol plant has been built to turn raw sugar into fuel, a commodity for which the world seems to have an insatiable demand.

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