Drainage Characteristics of Digested Sludge

The synthesis of an optimal design for a sludge drying bed will depend on the creativeness of the designer and, in part, on the availability of sufficient information on the several dewatering mechanisms of digested sludge. The paper is concerned with the drainage characteristics of digested sludge on sand beds and the influence of the type of construction of the sand bed on drainage. The maximum drainage rates, for drainage beds without ventilation, ranged between 1 and 5 l per day per ft², the higher values corresponded to a sludge height of approximately ≥ 12 in. The ten-day average drainage rate was approximately 1.2 l per day per ft² for sludge heights of 8 in. to 14 in. The maximum volume of drainage was associated with a sludge height of 8 in. and the value was 56% of the applied sludge volume. Ventilation of the sand beds resulted in greatly improved drainage. First day drainage rate for 8 in. of sludge was found to be 12 l per day per ft². For drainage beds provided with ventilation, covering to 50% of the sand bed surface did not reduce substantially the drainage rate nor the ultimate volume of drainage.