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Rajeb A.B.,Water Research and Technologies | Mehri I.,Water Research and Technologies | Nasr H.,Water Research and Technologies | Hassen A.,Water Research and Technologies
Clean - Soil, Air, Water

By considering its importance in biological wastewater treatment systems, biofilm formation over time and under activated sludge inoculation in a fixed biomass reactor was investigated. Experiments were conducted on a reactor composed of two successive PVC columns; a first gravel column and a second sandy one. The physico-chemical and bacteriological quality of treated water at the outlet of the biological reactor was tracked. Furthermore, a quantitative and qualitative study was made on the biofilm before and after addition of a carbon source. Thus, the attached volatile solid (AVS), exopolysaccharides (EPS), proteins (PN), and microbial DNA were quantified. The results showed that in the first column and at 80 and 168cm depth, AVS and DNA were greater than those registered at 5cm. A similar result was observed in the second column. Nevertheless, at the second sandy column and after sludge addition, the amounts of EPS and PN recorded at depth of 83 and 165cm were smaller than those obtained at 5 and 10cm of depth. On the other hand, the polymerase chain reaction-denaturing gradient gel electrophoresis method coupled with sequence analysis was used to survey the diversity of ammonia-oxidizing and denitrifying communities. The amoA gene sequencing showed that the majority of the ammonia-oxidizing communities was affiliated to Nitrosomonas. With the second column sludge addition, the denitrifying community seems to be affected. A great diversity of denitrifying bacteria in 168cm of depth was observed. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Ines M.,Water Research and Technologies | Yousra T.,Water Research and Technologies | Asma B.R.,Water Research and Technologies | Sana K.,Water Research and Technologies | Abdennasser H.,Water Research and Technologies
American Journal of Environmental Sciences

In recent years, certain strains of fluorescent pseudomonads called PGPB have drawn attention due to their abilities to promote plant growth. Therefore, in this investigation, we have explored the adhesive properties, the phytostimulator effects and the biocontrol activities of 40 isolates, with the aim to select potential inoculants to improve crop yields. Ten different colony morphotypes were detected on CRA plates. PsTp172 described as "ST" showed the highest adherence ability to abiotic surface (OD550 = 2.102). 31 isolates were positive for the plant growth-promoting hormone (IAA) production and 30 stains solubilised tri-calcium phosphate in Pikovskaya's agar. Furthermore, the highest pyoverdine concentration was detected with PsTp172 strain (172.50 μM) under iron starvation conditions. This strain also exhibited a coresistance against Zn2+ and Mn2+ and displayed high values of Minimum Inhibitory Concentrations (MIC) for each heavy metal. Additionally, among the tested isolates, eight strains (PsS15, PsTp172, PsS28, PsTp171, PsS31, PsS67, PsS18, PsS39 and PsS93) were found to be efficient antagonists against the 3 pathogenic strains and 6 isolates (PsS15, PsTp156, PsTp172, PsC54, PsTp171 and PsS102) were considered as lactone inhibitors of the 3 tested strains, as shown by their ability to inhibit the cellular communication. The majority of isolates showed various phytobeneficial traits and the most effective strains are P. putida (PsTp172 and PsS15) and P. mosseli (PsTp171). © 2014 Science Publication. Source

Rajeb A.B.,Water Research and Technologies | Kallali H.,Water Research and Technologies | Saidi N.,Water Research and Technologies | Abidi S.,Water Research and Technologies | And 2 more authors.
American Journal of Environmental Sciences

Problem statement: The current work study the efficiency of biological wastewater treatment by an aerobic reactor which could be used in small agglomerations. RBC reduced physicochemical and microbiological load of wastewater but values remain above Tunisian standard. Approach: Experiments were conducted on a sand filled PVC column fed with wastewater treated by Rotating Biological Contactor (RBC) at a pulsed rhythm of 8 sequences per day. For performances study process, physicochemical and bacterial analyses effluent at inlet and outlet of column were realized. Results: The results showed that through filter mass (D10 = 0.55 mm, D60 = 1.3 mm and coefficient uniformity = 2.36) 96% of suspended solids, 99% of NH 4 +-N (during first phase), 92% of COD, 91% of BOD5 and 46% of phosphorus are retained by surface filtration. The microbial abatement results is <1.6 Log units of indicators fecal contamination (fecal coliforms, fecal streptococci and E. coli). The microbial water quality is slightly higher than Tunisian standards. The removal of microbial indicators in the considered reactor depends on the depth of the filter and negatively correlated with NO 3 --N (r = -0.99, with E. coli at 3rd OPD). Conclusion/Recommendation: Results confirmed that the reactor tested is performed as an advanced treatment system for DBO, COD, SS, NH 4 +-N and NO 3 --N. Despite that 96% of SS efficiency reduction, clogging is not achieved quickly that due to biofilm detachment phenomena. The removal of microbial indicators in the considered reactor depends on the depth of the filter and negatively correlated with NO 3 --N. Disinfection performances for the considered reactor reduce microbial load, however chlore, ozone or UV disinfection should be considered. © 2011 Science Publications. Source

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