Patent SE-522886-C2 (SE)
Title: Treating effluent to reduce nitrogen, phosphorous and oxygen-consuming substances content comprises a multi step biological process using peat, combination of peat and bark, limestone and leca beads
Inventor: FORS KRISTER
IPC: C02F3/04
Filed: 1998-09-07
Abstract: A method for removing and recovering ammonium nitrogen to avoid nitrate or nitrite formation, and for removing and recovering phosphorous and oxygen-consuming substances (BOD) from leached water, effluent or the like, comprises a pre-filtration step to remove coarse particles and a multi-step filtration process with the filter media and control parameters adapted to provide effective biological, mechanical and chemical purification. During the filtration process the following steps are carried out : (1) peat or a similar biological material with acidifying properties is added during the first step in order to adjust the pH to 5.5, so that ammonia liberation and nitrification are prevented, phosphate solubility is increased and pathogens are killed ; (2) adsorption and cation exchange by the filter medium during the first and second steps is used to bind ammonia and prevent it from being liberated at high pH during the third step ; (3) pH in the third step is adjusted to ca. pH 9 using e.g. dolomite limestone supported a non-degradable material (e.g. mineral or glass wool) in order to chemically bond phosphorous, increase pH to maximise phosphorous bonding in so-called leca beads (or a material with the same chemical composition) and to kill pathogens ; (4) the BOD/nitrogen ratio is maintained at a given level during the first and second steps in order to give optimum heterotrophic bacteria growth and incorporation of ammonium nitrogen into the bacteria cells ; (5) BOD is quickly reduced in a peat filter medium or the like in order to increase enzyme production by the bacteria and therefore increase phosphorous solubility in water, giving improved phosphorous bonding in the third step ; (6) oxygen supply is regulated to give a high microbiological activity, so that most oxygen is used during the first step, giving a low oxygen concentration of less than 4 ppm in order to hinder nitrate formation during the second and third steps, reduce bacterial production and growth in the third step, and reduce the biomass from lysed bacteria to prevent the third step being repeated ; (7) a filter medium with a high surface area for bacterial growth is used during the first and second steps ; (8) the filter medium used during the first and second steps can absorb 20-40 % of its own volume of water in order to give effective biological purification with regards to nitrogen and phosphorous ; (9) a top layer of coarse peat fibres or similar material with a supply of oxygen from the atmosphere to the so-called biofilm, and a bottom layer of finer peat particles or the like with a supply of oxygen to its base from a supply means is used to form the filter medium in the first step ; and (10) the filter medium in the second step comprises a peat material or the like for microbiological incorporation of phosphorous and nitrogen and BOD reduction, in addition to a medium such as bark for increasing pH to provide better bacterial growth conditions.