Sewage treatment plant at the Worme Hofgemeinschaft in Handeloh

Decentralized purification plants are particularly suitable for remote farms and hamlets in country areas.

‘O’er seven stones the water flows,

’tis pure again, the farmer knows.’ This piece of agricultural wisdom may well no longer apply to the present day and the highly complex ways in which water is now polluted, but there is a grain of truth in it: water is able to purify itself. Nothing has changed here. But cities have long since had to say goodbye to giving sewage the time and space to purify itself. They have ultimately arrived at narrow-mesh sewerage networks and treatment plants, via the intermediate stage of evil-smelling sewage farms. This is a hygienic but very expensive method of getting rid of the daily quota of faeces.

Since the early 1990s, country people have increasingly started to remember decentralized sewage treatment. An increasing number of farmers, but also private householders who have enough land, are letting their sewage flow not over seven stones, but through settling tanks and purification beds, so that it can then pass into an effluent tank having been cleaned. This also applies to the Hofgemeinschaft in Worme, an organic farm in Handeloh, south of Hamburg. The Dreiseitl studio planned a sewage treatment plant for about 30 people who live there plus holiday visitors and participants in educational projects.

The planners took advantage of the natural slope on the site, and were thus able to do without technical units to a large extent. Thus sewage from the farm first flows into a 250 metre long collector tank and then into three shafts. Here a filter sack separates solid and liquid components. Alternate use of the shafts means that the contents of the filled bags can be pre-composted and used in fields and gardens after nine to fifteen months.

The liquid part then flows into purification beds with an area of 7 square metres per resident equivalent. The botanical treatment plant is de-

Fitting the sheet seal in a purification bed. Here laymen can help as well – a school class at work.

Setting the manholes and introducing the filter substrate

The decentralized treatment plant with purification beds treats all the sewage from the hamlet of Unterbach, which has 80 inhabitants.

Installing the substrate for a purification bed layer by layer

Planting the beds with aquatic plants (phragmitis)

Sewage treatment plant at the Worme Hofgemeinschaft in Handeloh

signed for a maximum of 100 resident equivalents. The sewage runs through the beds in two stages: first of all through four 80 centimetre deep beds arranged in parallel, with a infiltration length of 5 metres. In the second stage the beds are 1 metre deep with a infiltration length of 7 metres. The plants that grow there introduce considerable quantities of oxygen into the earth- or water-bearing layer. Aerobic decomposition processes are then set in train. After passing the sampling shaft the purified sewage runs into the little river Seeve via a semi-natural channel with plants growing in it. Very little care and maintenance has proved to be necessary. The purification beds have simply to be kept free of undesirable vegetation and woody plants. The pipes and gutters have to be flushed out three to four times a year to test and maintain their ability to function.

The plant has been working without problems, economically and without complaint since 1994. The Worme farm’s treatment plant has thus contributed to regional water quality, but also considerably reinforced its image as an organic farm and seminar venue.

Sewage treatment plant at the Worme Hofgemeinschaft in Handeloh

Residents can service the plant themselves, as it is easy to manage; this gives people long-term responsibility for their own sewage disposal.

The sewage seeps through several planted tanks and harmful substances are removed by organic decomposition processes at the various purification stages.

Sewage treatment for an agricultural establishment with nursery

Section through the various purification stages: sewage flows horizontally through plant filters.

Sewage treatment plant at the Worme Hofgemeinschaft in Handeloh