Colsen maximizes energy revenu of WTTP Den Bosch (NL)

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By JaapK

The demands for modern WWTP's to operate more sustainable are becoming increasingly stringent. This applies in to many of the WWTP in The Netherlands and also to the Treurenburg location in Den Bosch (NL), which is owned by Water Council Aa and Maas. In order to achieve the desired performance, specific technologies must be applied. Colsen owns a broad range of technologies which have been applied to the sludge line at the WWTP in Den Bosch to be able to more efficiently process the sludge stream and to maximize energy output in the form of biogas. Below the various technologies are further described.

Thermophilic Digestion
One of the technologies is thermophilic digestion, which comprises an efficient method for the digestion of organic residues in waste streams. The bacterial sludge decomposition normally occurs at mesophilic temperatures (between 35 and 38°C). In the Den Bosch case the combination Besix-Hegeman has chosen for thermophilic digestion under conditions of slightly higher temperatures (between 50 and 55°C). Under thermophilc conditions the decomposition process is much faster and the yield is much higher. There are two important parameters that must be taken into account. The temperature must be kept between strict boundaries and the sludge present in the reactor must be continuously mixed. The Colsen DIGESTMIX®-system is taking care of that.

The technologie behind our DIGESTMIX® is characterized by a combined mixing/heating principle. The installation is mounted at the exterior of the reactor. The mixing tubes assure a high flow and guarantee full mixing of the tank content during multiple times per day. The tubes effectively facilitate the heat exchange such that the temperature in the reactor remains under strict control. Because all equipment and technical parts our mounted external of the tank, maintenance does not require the reactor to be emptied. The DIGESTMIX® system mixes and heats the content of the reactor at minimal cost for energy and maintenance.

Another technology that Colsen has implemented within the sludge line is the ANPHOS®-process, through which phosphate is recuperated in an environmental friendly manner from waste water after the sludge de-watering step. During the biological decay of sludge as a result of thermophilic digestion Phosphorous is liberated as ortho-phosphate, whereas Nitrogen is set free in the form of ammonium (NH₄-N). These are precipitated in the ANPHOS® reactor. In this way only small amounts of phosphate flush out of the waterline and in the meantime struvite precipitation in piping is prevented. As a result we are capable of reclaiming phosphate from the waste streams with the option to be used elsewhere (e.g. as a fertilizer).

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Biogas is desulphurised in the Bidox® installation

The biogas produced during digestion contains significant amounts of H₂S, which can be harmful when applied directly in gas engines and boilers. With intervention of the Colsen BIDOX® technology the H₂S is removed from the biogas via a biological pathway. Bacteria are taking care of the transformation of this substance, thus preventing unnecessary operational costs for the end user of the gas. The resulting biogas is directly suitable for users, as in this case for the Heineken breweries. Through the implementation of the above technologies Colsen has claimed a major contribution to the sustainable, eco-friendly and energy-efficient footprint of the WWTP in Den Bosch.

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