A moving bed biofilm reactor for nitrate removal from drainage water by KU Leuven
KU Leuven is testing a Moving Bed Biofilm Reactor for removal of nitrate from drainage water in Onze-Lieve-Vrouw-Waver.In Flanders (the North part of Belgium), the most open agricultural fields are provided with a drainage system to collect the runoff water and discharge it into the local surface water streams. So, in a period with a lot of precipitation, the soil gets saturated and then the drainage water (excess runoff water) starts flowing. The so-called drainage season starts typical in October and can last until April or May. The drainage water has a high nitrate content because unused fertilizers leach out into the drainage water.
In this field case, the drainage water of two runoff areas (1.43 ha, see Figure 1) was characterized with an average concentration of 30.7 mg NO3-N/L, exceeding the EU standard of the receiving surface water, i.e., 10.3 mgNO3-N/L. Specific issues determine the choice of technology used to treat the drainage water:
- Low water temperatures (between 5 – 15 °C)
- Variable flow rates and nitrate concentrations
- Simple and low budget system
- Limited footprint
Therefore, a Moving bed biofilm reactor (MBBR), using plastic carriers (AnoxK™5) on which a denitrifying biofilm will grow, has been selected in this study.
Based on historical measurement data of the catchment area (flow rate and temperature), a plant was designed to handle 1000 L/h of drainage water with a nitrate concentration of maximum 45 mg NO3-N/L (=200 mg NO3/L).
AnoxKaldnesTM Carriers type K5 (AnoxK™5) were chosen, and this mainly because this type of carriers possesses a very high specific surface area of 800 m2/m3 for biofilm attachment. The greater the specific surface area of the biocarriers, the greater the degradation capacity per m3 of MBBR volume. To be able to meet the most extreme conditions, an underground concrete anoxic MBBR system of 15 m3 (Figure 3 (a-c)) filled with 4.4 m3 of AnoxK™5 (Figure 3 (d)) was installed on the pilot site in Onze-Lieve-Vrouw-Waver.