ANTI-EROSION CAPACITY OF A GRANULAR FILTER SUBJECTED TO A PERIODICALLY VARIABLE HYDRAULIC GRADIENT

The instability of a filter system is a significant cause of seepage failure in embankment projects. The filter system in the earth-rock embankment is mainly composed of graded cohesionless soil. To uncover the performance of the granular filter in resisting the internal erosion, a set of experiments was carried out with an improved experimental apparatus, considering different hydraulic loading scenarios. The movement of graded cohesionless soil, the seepage velocity and the hydraulic gradient were monitored in the experiments. It was found that during the process of increasing the hydraulic gradient, the failure of the granular filter mainly experienced three stages: the first one was the dynamic equilibrium stage; the second was the critical start stage; and the third was the failure stage, in which a sudden change in the seepage velocity was the precursor of seepage failure. The critical hydraulic gradient and destructive hydraulic gradient decreased with the water level amplitude. Moreover, the experiments revealed that the loading modes of the hydraulic gradient significantly influenced the anti-erosion capacity of the granular filter. Compared with the stepwise loading mode, the cyclic reciprocating loading mode greatly weakened the anti-erosion capacity of the granular filter under the same water level amplitude. The destructive hydraulic gradient of the latter was only 71.8 % of the former under a higher water level amplitude, indicating that the corresponding measures should be considered to avoid the occurrence of a periodically variable hydraulic gradient.

Chemical, Physical and Biological Carwash Wastewater Treatments for Water Recycling: Critical and Comparative Analyses

The carwash industry uses large volumes of freshwater and release wastewater containing harmful chemicals into the environment. The type and quantity of cleaning chemicals and finish products used and the amount of dirt present on the vehicle affect the physical, chemical and biological characteristics of the carwash wastewater. The growing public concerns for water conservation and the environmental health of water waterways has led to several environmental regulations to encourage wastewater reclamation and reduction of pollution loads. The environmentally friendly carwash operation requires a good washing technology with compatible washing chemicals and advanced water treatment methods with proper water recycling system. The desire of professional carwash operators to conserve water and/or reduce discharges dictate the choice of approach and reclaim equipment to be installed. This study describes the treatment options for carwash wastewaters for recycling in order to achieve pollution reduction, water conservation and economic benefits for carwash operators. These treatments include chemical coagulation-flocculation, electrocoagulation, electrooxidation, granular filtration, microfiltration, ultrafiltration, nanofiltration, reverse osmosis, biofilters, bioreactors, wetlands and adsorption. The advantages and disadvantages of each method were determined. Each method was evaluated and compared with other methods using a standard set of criteria that included: cost, maintenance and control, efficiency, suitability, value added product, environmental and health impact and size and land requirement. These criteria were developed based of the advantages and disadvantages of the treatment methods. Each criterion was assigned a score based on its relative importance. A comparative analysis was performed on the 12 methods of carwash wastewater treatments using the eight criteria. The results indicated that granular filter treatment had the highest score (87) followed by reverse osmosis (84). It is therefore recommended that a combination of granular filter and reverse osmosis be used to treat carwash wastewater. The granular filter is used as a pre-treatment option to remove suspended solids, heavy metals and pathogenic microorganisms and the reverse osmosis unit is used as a final treatment for polishing the granular filter effluent and remove all remining organic molecules, cysts, bacteria, virus and all minerals including dissolved individual ions. The final product is a spotfree rinse water resulting in glass, chrome, and all painted surfaces to dry spot-free. Granular filter is easy to set up using locally available material, is economical and has a low capital and operating cost and a short residence time and can achieve reductions of up to 100% of COD, TSS and turbidity. Reverse osmosis results in complete removal of pathogens and virus and up to 99 % removal of dissolved solids.

A REVIEW ON THE APPLICATION OF GRANULAR FILTER MEDIA AND THE UTILIZATION OF AGRO-INDUSTRIAL WASTES FOR STORMWATER QUALITY IMPROVEMENT

The stormwater management practices have changed from conveyance-oriented to storage-oriented, as part of the Best Management Practices (BMPs). Still, uncontrolled development increases potential pollutants in the stormwater, which conveys into a water body or river. Continuous improvements in the filtration mechanism would complement stormwater management. For the past decades, there is progress in applying granular filter media for stormwater quality improvement. However, the reports were not systematically reviewed. In this paper, the recent five years research that utilizes granular filter media for improving stormwater quality was retrieved and reviewed. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) was referred to, where Scopus and Web of Sciences, two primary journal databases, were used. Initially, keywords searching strings have resulted in 467 articles, which were further screened. Four themes have been formed: stormwater management, stormwater characteristics, separation mechanisms, and future perspectives. Next, two sub-themes and two sub-sub-themes were further established. Then, 65 articles were included manually to complement the themes developed to explore the potential agro-industrial wastes as sustainable filter media. Therefore, this review has proven that the relatively inexpensive and renewable resources from the agro-industrial wastes can remove pollutants efficiently from the stormwater. Four main criteria affecting filter media performances are also highlighted, including the grain sizes of the media, media bed configuration, hydraulic loading rate, and the suspended solids concentration. Further study on these variables can be beneficial to explore the impact of utilizing agro-based media in stormwater filtration.

Determination of hydraulic conductivity for granular filters based on constriction size and shape parameters

This experimental study is an attempt to apply the constriction size concept for determination of hydraulic conductivity of filter material. Five shapes of granular filter material having varying gradations were used for the experimental investigations. The controlling constriction size of selected shapes having varying gradations were worked out and related to the experimental results of hydraulic conductivity. The empirical model for hydraulic conductivity determination based on controlling constriction size for each selected shape of granular filter material was developed. Finally, a combined empirical model for the determination of hydraulic conductivity of granular filters was developed based on shape parameters and the controlling constriction size.

Investigation of the Efficiency of a Granular Filter Based on Cement Clinker

The article describes the process of cleaning dusty gases. Attention is paid to the devices for fine cleaning of dusty gases. Attention is focused on the fact that the most simple and, at the same time, effective dust cleaning device is a granular filter. Its advantage is shown when cleaning dusty air from very aggressive devices, when working on high-temperature and aggressive gases. The prospects of granular filters, in which a cement clinker is used as a filter material, with a granule size of up to 10 mm, are shown. The main causes of dust deposition on grains, filaments or fibers are presented. Various approaches to determining the empirical dependences of the dust span on the design parameters of the filter apparatus are presented. The criterion dependence of the cement dust span is presented, which approximates the results of the experiment. It allows you to determine the efficiency of the granular filter from its design and technological parameters.