Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Impact of pre-treatment of primary effluent on clogging and removal of nutrients during soil aquifer treatment

Auteur : Ntelya J.P.

Université de soutenance : UNESCO-IHE Institute for Water Education, Delft

Grade : Master of Science 2012

Résumé
Rapid population growth, increasing water demand, urbanization, climate change, and over extraction of groundwater aquifers will cause massive pressure on water resources in future. Many arid and semi-arid regions in the world are currently moving towards the limit or have already reached the limits of their available water resources. In due course water is becoming a scarce commodity in these regions. To overcome water scarcity issues around these regions, there is a need to reuse pre-treated municipal wastewater effluents. Natural treatment systems (NTS) such as soil aquifer treatment (SAT) are some of the technologies that are attractive for application in developing countries. The mechanism of removal of contaminants from primary effluent (PE) during SAT is not fully understood. Laboratory-scale soil column experiments were conducted using column with silica sand (size 0.8 to 1.25 mm) used as a filter media and fed with PE and coagulated primary effluent (PE+COAG) at different hydraulic loading rates (HLRs) were used to evaluate and compare the removal of bulk organic matter, nutrients (phosphorus and nitrogen) and pathogens. The overall DOC removal from PE at HLRs of 0.625 m/d and 1.25 m/d were 60% and 51%, respectively. For PE+COAG, DOC removals at HLRs of 0.625 m/d, 1.25 m/d and 2.5 m/d were 61%, 60% and 54%, respectively. The average total nitrogen removal during soil column experiments with PE+COAG at HLR of 0.625 m/d was relatively high (63%) compared to PE at HLRs of 0.625 m/d (30%) and 1.25 m/d (15%). Additionally, it was also high as compared with PE+COAG at HLR of 1.25 m/d (34%), and 2.5 m/d (43%), respectively. Phosphorus was efficiently removed from PE and PE+COAG at the lowest HLR of 0.625 m/d. The removal of phosphorus from PE at HLRs of 0.625 m/d and 1.25 m/d were 54% and 17%, respectively. On the other hand, phosphorus removal from PE+COAG at HLRs of 0.625 m/d, 1.25 m/d and 2.5 m/d were 84%, 35% and 20%, respectively. E-coli and Total coliform were able to be removed in the range of 2.5 to 3.7 log removal within 4 m column depth with PE and PE+COAG at different HLRs under aerobic conditions. The PE+COAG at HLRs of 0.625 m/d and 1.25 m/d demonstrated less amount of head loss development and clogging effect in the first 50 cm of about 1.5 cm/d and 2.2 cm/d as compared to 5.7 cm/d and 5.1cm/d with PE at HLRs of 0.625 m/d and 1.25 m/d espectively. However, high head loss development of about 16.9 cm/d was observed with doubled infiltration rate of 2.5 m/d in the first 50 cm of soil column as the results of increasing loading rate of organic and inorganic suspended material on the surface of soil column. Based on the finding of this research, coagulation of PE before SAT application at lower HLR was found to be the best alternative with respect to the reduction of soil clogging, removal of bulk organic matter, nutrients and pathogens.

Mots clés : nutrient removal ; soil aquifer treatment ; effluents

Présentation