In the above comparison between natural and artificial treatment reference has been had chiefly to the aerobic branch of the business, but the anaerobic, breaking down _some_ of the solid organic matter and the sanitary disposal of the remainder in the state of sewage sludge (containing fully 90 per cent. of moisture) must not be overlooked or shirked as beneath the attention of the scientific bacteriologists and chemists whose analyses of effluents, and often of what they call crude sewage, are made from the liquid which has passed through a filter paper in their laboratory before their “oxygen absorbed” or “ammonia processes” are proceeded with.
On the contrary, I have always maintained that sludge, being the foulest part of town sewage, ought to receive primary and earnest attention if we desire to improve the condition of our watercourses.
When town sewage is pumped through a long rising main, it can often be spread on the land in its really crude state, and if the soil is clay ploughed up to receive it the sludge is most beneficial to its texture.
But in every other case we must face the nuisance of extracting the sludge, and its desiccation in one of the following ways.
1. On a farm at some distance from roads and houses, the cheapest plan is to form a bank of earth about 18 inches high, enclosing a rectangular area into which the wet sludge can be run or pumped out of depositing tanks, and left alone until dry enough for cartage, when it can be used on the farm or sold to neighbouring farmers for a shilling or two a load.
2. A wall of farmyard _long_ manure may be used instead of earth, and trench 5 feet wide dug on each side of the longer sides of the rectangle, leaving 3 feet of ground between the wall and trench, on which men can stand to scoop the sludge over the wall when it has consolidated a little in the trench; the latter is then ready to receive the sludge from another tank emptying, which is again scooped over the wall on to a thin coating of farmyard manure, which has been scattered over the last layer of sludge in the rectangle; and thus in a year’s time a solid mass of the mixture is raised four or five feet high, and is in capital order for putting in drills for a crop of mangold wurtzel.