The CAMBI process and agriculture, a sustainable solution?
Both public acceptance and interest from farmers for spreading biosolids from waste water treatment plants (wwpt) on arable land, are dependent on some fundamental criteria. These criteria are, however, quite straightforward. The biosolids should be safe, easy to handle, a well documented source of plant nutrition, without disagreeable odours and easily available. A big part of the opposition to agricultural use of biosolids has been based upon the appearance and the odour of the product. In this study, five plants using the Cambi Thermal Hydrolysis Process (THP) have been investigated. The paper summarizes the experiences of applying biosolids in agriculture. It also includes experiences from a plant that treat pure catering waste. The Cambi Cake biosolids (Cambi THP + anaerobic digested + dewatering) has proven to be a stabilized, plant nutritious, low-odour, product resembling compost and is popular with farmers. The popularity is also due to its ability to be stored outdoors without causing unpleasant odour, low risk for nutrient loss because of high dry solid (DS) content, and can be applied when needed. For wwtp that also have thermal drying of biosolids, the experience is that farmers seem to prefer the Cambi Cake For wwtp the introduction of Cambi THP has caused 50 % less biosolids to be stored and spread compared to conventional anaerobic digested and dewatered biosolids. This is based on the fact that Cambi THP increases the degradation of organic matter and the digestate dewaters well. Levels of heavy metals and organic micro-pollutants will still be of concern along with concerns regarding eutrophication caused by nutrient runoff. These concerns need to be addressed. However, reservations because of odour and uncertainty in connection with hygiene are not of any concern for the farmers who apply Cambi Cake on agricultural soil.