Sustainable and low-cost Ocimum gratissimum for biosorption of indigo carmine dye: kinetics, isotherm, and thermodynamic studies.

In the quest for a sustainable environment and clean water resources, the efficacy of Ocimum gratissimum leave (OGL) for indigo carmine (IC) dye biosorption was studied in a batch technique. The physicochemical properties of OGL supported its suitability for biosorption studies. Of 92.6% removal efficiency was achieved at optimum conditions of pH 2, contact time 120 min, initial IC concentration 500 ppm, temperature 298 K, and 100 mg OGL dose. Kinetic data were best fitted to pseudo second-order (PSO) and the mechanism was pore diffusion governed as validated by sum of square error (SSE) and non-linear chi-square (χ 2). Freundlich isotherm model gave the best description at 298 K as supported by Halsey, Redlich-Peterson, and Fowler-Guggenheim confirming the heterogeneous nature of OGL and multilayer biosorption process. Langmuir Q max (77.52 mg g-1) surpassed those previously reported. SEM and EDX confirmed the reality of the biosorption process. Thermodynamic parameters (ΔH°, ΔS°, ΔG°, and Ea) affirm a feasible, spontaneous, exothermic, and randomness of the process. Results revealed that OGL is a potential and efficient environmentally benign, low cost, and sustainable biosorbents. It is therefore recommended as a bi-functional biosorbent for wastewater treatment.

Influence of water repellent chemical additive and different curing regimes on dimensional stability and strength of earth bricks from termite mound-clay.

This article is focussed on evaluating the effects of water repellent admixture and different curing regimes on characteristics of clay from termite hills used for production of earth bricks. Water absorption, thickness swelling and compressive strength characteristics of the specimens with different compositions of cement, hydrated lime and water repellent additive subjected to different curing regimes were measured. The samples were characterised by SEM and FTIR. The least water absorption was at 3.3% while thickness swelling ranged from 0.78 to 3.21 % for the samples. Saturated curing condition resulted in an average compressive strength of 35.5 N/mm2, cured curing recorded an average value of 32.9 N/mm2 while dry curing condition produced an average compressive strength of 26.9 N/mm2 and the wet curing condition resulted in 25 N/mm2. SEM characterisation of sample containing 70% termite soil, 30% cement and 0.05 Hydropruf indicated fewer voids, regular and smooth appearance in comparison with others. FTIR analysis showed distinctive broad bands at wave numbers of 3439 cm-1 for O-H stretching, and 1033.83-1008.80 cm-1 for O-H bending for all samples tested. The best performing composition in terms of the dimensional stability test was 70% termite mound clay, 10% cement, 20% hydrated lime and 0.05 Hydropruf additive. The highest mechanical strength was from composition of 70% termite mound clay, 30% cement, no hydrated lime and 0.05 Hydropruf additive. It is concluded that saturated and cured method showed better performance than the wet and dry curing regimes. The termite secretions similarly improved the clay composition in conjunction with cement, lime and chemical admixture in the internal structure of the bricks.