In order to optimize sludge depth in sand drying beds under the climatic conditions of Saudi Arabia, the effect
of sludge initial depth on the physical and chemical characteristics of dried municipal sludge samples was investigated.
The investigation was carried out for one year at Al-Khobar Wastewater Treatment Plant, where initial sludge depths of
10, 15, 20, 25, 30 and 35 cm were implemented. Sludge samples were collected after 0, 1, 2, 4, 7, 14, and 30 days of
drying and were analyzed for certain potential parameters such as total solids, oil and grease, and heavy metals. The study
showed that the effect of the initial sludge depth in drying beds on the physical and chemical characteristics under
investigation was apparent in some cases, while was not clearly demonstrated in others. As an example, the reduction of
initial water content, in 30-day dried sludge samples, was increased from 43.8 to 51 percent as the sludge initial depth was
reduced from 35 to 10 cm, respectively. On the other hand, the effect of initial sludge depth on the pH, alkalinity, oil
content, and concentration of heavy metals was not clear and did not show a consistent pattern.