6th March 2005 at 12:07 pm #618
Actually, lower saturation of oxygen at higher temperatures doesn’t mean it disappears easily. At higher temperatures, air is less dense and therefore contains less oxygen. Furthermore, it is my guess that warmer water can not hold as much dissolved oxygen as cold water.
Regarding the depth of the sand column, Buzunis actually suggests that the biological zone in intermittent sand filters is shallower. Hence, a shallower sand column could be appropriate. This contradicts our earlier conclusion about a minimum of 60 cms to be on the safe side. Probably the best design would include the following:
– Supernatant water level as low as possible, because this allows diffusion of oxygen to a deeper level into the sand. Literature research or testing needs to prove whether a low level disturbs the schmutzdecke, leading to decreased biological performance. This would seem probable. If so, then there will be a trade-off level of supernatant water that allows maximum diffusion and least disturbance of schmutzdecke.
– Buzunis also mentions that most biological removal takes place during the pause times when no water flows through the filter. Once more than 10 litres have gone through his filter, having replaced all water previously inside, his graphs show an increase in ecoli.