Study of the prospects for agricultural utilization of sludge produced from WWTPS in North Central Algeria

Abstract

The objective of this study is to investigate the sewage sludge of six wastewater treatment plants (WWTPs) in North Central Algeria for agricultural reuse. After a brief description of the region (climate, distribution of soils, and crop types), a quantitative and qualitative examination of the sludge produced was conducted in addition to a comparative study of urban compost and cattle manure. The selected agronomic parameters were dryness, percentage of organic matter (OM), as well as the contents of nitrogen, phosphorus, potassium, and calcium. An average OM of soils of 1.3% and a minimum value of 0.2% made it clear that the urgency of providing this type of amendment was warranted. The sewage sludge in this study was characterized by carbon to nitrogen ratios lower than those of manure and compost due to its stabilization process at the WWTPs on one hand, and the presence of recalcitrant lignin compound mineralization in compost and manure, on the other hand. The spreading of sludge in the region covered a very small surface area, not exceeding 0.50% of the overall agricultural area. The quantities of fertilizers produced by sludge were significant and often exceeded agricultural requirements. Yet, due to the insufficient amounts of OM provided by sewage sludge, there was a need to rely on alternate sources such as manure and/or urban compost.

Keywords:

• Recovery
• Sludge
• Organic matter
• Fertilizers
• Safety

Acknowledgments

This work was conducted in the Research Laboratory of Water Sciences at the National Polytechnic Institute of Algiers, in collaboration with the laboratories of three agencies listed below. The authors would like to thank and acknowledge the support of these agencies which facilitated access to their documentation as well as to the analytical data of the parameters required for this study.

(1)	ONA (Office National d’Assainissement) at the Kolea, Boumerdes, Medea, and Tipaza WWTPs.
(2)	SEAAL (Société des Eaux et de l’Assainissement d’Alger) at the Beni-Messous WWTP.
(3)	SARL VaTech WABAG GmbH at the Reghaia WWTP.