JWSS - Journal of Water and Soil Science

The goal of this study was to evaluate tannic acid as a coagulant in turbidity removal. Tests were designed using Taguchi method and carried out on the synthetic and natural turbid samples. In order to optimize turbidity removal by tannic acid, seven factors including pH, coagulant dosage, rapid mixing rate, slow mixing rate, slow mixing time, sedimentation time and initial turbidity were investigated. The results revealed that in optimum conditions,  tannic acid could n remove up to 71 percent of synthetic turbidity and 66 percent of natural turbidity; also, tannic acid showed more coagulation activity in the lower initial turbidities. ANOVA analysis showed that initial turbidity and slow mixing time were the most important parameters in the turbidity removal by tannic acid. In general, this study showed that tannic acid was capable of removing turbidity and could be used instead of common coagulants in the preliminary treatment.

In general, engineering designs need to optimize the factors affecting the under-study phenomenon; however, this is often a costly and time-consuming process. In this regard, new methods have been developed to optimize with fewer tests; thus, they can make the whole process more affordable. In this study, Taguchi and Taguchi-GRA methods were used to design the geometric parameters of the protective spur dike in order to optimize their efficiency in reducing the scouring in a series of spur dikes. The results of both methods showed the optimal ratio of the length of the protective spur dike to the length of the first spur dike was 2.5 and the angle of the protective spur dike was 90 °. However, the ratio of the length of the protective spur dike to the length of the main spur dike in the Taguchi method was 0.8 and in the Taguchi-GRA method, it was 0.6. In addition, using variance analysis showed that the distance between the protective spur dike from the first spur dike, the protective spur dike angle, and the length of the protective spur dike were, respectively, the most effective on the performance of the protective spur dike. The results of this study, therefore, indicate that both methods are highly effective in optimization and, therefore, can be useful in the hydraulic engineer studies.

In the last few decades, the use of porous concrete to cover the sidewalks and pavements as an interface to collect the urban runoff has been increased. This system is economically more efficient than other runoff-pollution reduction methods. To design a runoff control system and reduce its pollution, it is necessary to determine the hydraulic and dynamic properties of the porous concrete (with and without additives). In this research, the effects of cement type (2 and 5), water to cement ratio (0.35, 0.45 and 0.55), fine grains percent (0, 10 and 20%), the type of additive (pumice, industrial pumice, perlite and zeolite), and the added additive percent (5, 10, 15 and 20%) on the physical properties of the porous concrete (porosity, hydraulic conductivity and compressive strength), each with three replications,  were  investigated using robust design. Qualitek-4 software was also used to discuss the results. The results showed that to obtain the highest porosity in the mixing scheme of the porous concrete, no fine grains, cement type 2 and 15% industrial pumice should be used, and water to cement ratio should be 0.35. Also, the water to cement ratio of 0.55, 0% fine grains, type 2 cement and 15% industrial pumice resulted in the highest value of hydraulic conductivity in the porous concrete. Finally, the water to cement ratio of 0.55, 20% fine grains, type 2 cement and 5% zeolite led to the maximum compressive strength. In general, it was not possible to reach a logical conclusion in this research with the least costs without employing the robust design.