Abstract
Transport of Cryptosporidium in runoff will contaminate the surrounding water body. Cryptosporidium-sized microspheres and inactive Cryptosporidium parvum oocysts removal using an active carbon (AC) filter with/without coal gangue from the runoff was evaluated. Chemical composition of coal gangue was determined, and its performance as a water treatment material was tested. Results showed SiO2 was the dominant chemical component of coal gangue. Removal was only 20% for microspheres and 24% for oocysts by AC filtration alone. The removal for both was increased to more than 98% by addition of coal gangue powder to the filter. Furthermore, gangue reuse turned commercially worthless material to a water treatment material as well helping prevent gangue from occupying agriculture/industry land.
1. Introduction
Coal gangue makes up 10% to 25% of the amount of coal yield in China, which turns to industrial wastes congregating like huge mountains in coal mining areas. In mining, gangue is the commercially worthless material and thus distinct from overburden, the waste rock or materials overlying an ore or mineral body that are displaced during mining without being processed. More than 1,600 coal gangue mountains with approximate 45 million tons of gangue are found in China. The number of gangue mountains is still increasing with the accumulation of 1.5 to 2 million tons/year. Gangue reuse rather than dumping as tailing will help to manage the waste in coal mining area and may later find a commercial use. So far, there is no reuse research on coal gangue as a water treatment material to remove Cryptosporidium from water.
Cryptosporidium is one-celled intestinal parasite with diameter of 4–6 μm and has been reported for contamination of water worldwide [1–3]. Transmission of Cryptosporidium via runoff to surface water is relatively common. However, there is limited research on Cryptosporidium removals from runoff so far.
AC filters are effective for removal of multiple contaminants from water body [4, 5]. They are easy to install and less maintenance is required. The runoff in research area contains multiple pollutants, such as protozoan pathogen Cryptosporidium and polycyclic aromatic hydrocarbons. Here, AC filter was selected due to its large specific surface area with high adsorption. However, Cryptosporidium removals by AC filter were low indicated by the preliminary experiments. In this paper Cryptosporidium-sized microsphere and inactive Cryptosporidium parvum oocyst removals from runoff were evaluated by AC filter with/without coal gangue powder, intending to enhance the AC filter performance.
2. Methods and Materials
2.1. Experimental Methods
Figure 1 shows the lab-scale AC filter and runoff treatment system. AC filter height was 0.5 m and diameter was 0.5 m. The filtration rate was 20 m/h. The filter was backwashed every 24 hrs. Online data could be recorded and downloaded from a computer. A control experiment without gangue powder was conducted. Duplicate experiments were conducted and triplicate samples were collected.
Gangue and soil samples were collected from a local coal mining area. It was crushed into small grain (10–30 mm) and then ground into powder (5 μm) by a grinding machine (LHE-1000, Zhengyuan Company, Shandong, China). The gangue powder was stored in dry basket for use. Chemical composition was tested by X-ray Fluorescence (XRF, EDX8800E, 3V Instrument Co,. Ltd, Suzhou, China). The gangue powder solution (volume ratio of powder/water = 1 : 2) was fed previous to experiment by circulation pump.
The use of polystyrene microspheres as an oocyst surrogate has been done by multiple researchers, and it was used in this study [6–13]. Microspheres with diameter of 4.5 μm were used as the surrogate (Fluorsebrite™ Carboxylate YG 4.5-micron microspheres, Cat. #16592, Polysciences, Inc., Warrington, Pennsylvania, USA). Heat-inactivated C. parvum oocysts were used. Oocysts were heat-inactivated at 55°C for one hour prior to seeding. The concentration for both stocks was 4 × 1011 #/L. Samples were passed through 2.5 μm pore size filters. Each polycarbonate filter was mounted on a glass microscope slide under an epifluorescent microscope at 100x magnification. C. parvum samples were concentrated by centrifugation twice at 4,000 g at 4°C for 15 minutes followed by two microcentrifugation steps at 15,000 g at 4°C for 5 minutes and detected under 200x magnification [14].
Approximately 107 (1.82 #/mL) microspheres and oocysts were fed. Filter influent and effluent samples were taken for removal calculation. Runoff combined with microspheres and oocysts were fed. Duplicate experiments were conducted. Triplicate samples were taken for each.
3. Results and Discussion
Collected gangue chemical composition is shown in Table 1. Varieties of mineral substances were found in coal gangue, which contains SiO2, Al2O3, Fe2O3, CaO, MgO, Na2O, K2O, SO3, P2O5, C, N, H, and so forth. The max-composition was SiO2 which took up 30% to 60%, while Al2O3 (20% to 30%) took the second place, followed by C, MgO, and Na2O. In addition, heavy metal concentration in coal gangue and soil was compared and shown in Table 2. Cadmium, lead, mercury, chromium, arsenic, and copper were found in coal gangue. Similar heavy metal concentration was observed between gangue and soil. The metal concentration in coal gangue and soil was below the Chinese Environmental Protection Agency limits (GB15618-1995).
Figure 2 shows the microspheres and oocysts removal with and without gangue powder addition on the surface of the AC filter. Average removals were 23% (varied from 16% to 34%, standard deviation = 0.07) and 24% (varied from 14% to 26%, standard deviation = 0.05) for microspheres and oocysts by AC filter, respectively. The average microsphere and oocysts removals were 99% (varied from 97% to 99.9%, standard deviation = 0.01) and 98% (varied from 95% to 99%, standard deviation = 0.02) by AC filter with gangue powder on its surface (duplicate experiments and triplicate samples). Removals of microspheres and oocysts were similar demonstrating that the microsphere was an adaptable Cryptosporidium surrogate. There is rare research on Cryptosporidium removal from runoff. The removal as high as 99% can be comparable with the removals of Cryptosporidium by sand filter with coagulation [15]. However, the mechanism was different from coagulation followed by sand filtration. The potential reason of gangue powder enhanced AC filter performance is similar to membrane filtration.
4. Conclusions
AC filter could remove 23% of Cryptosporidium-sized microspheres and 24% of oocysts. The AC filter with gangue powder achieved 99% microspheres and 98% oocysts removal. The results indicated AC filter with coal gangue power could remove microspheres or oocysts from runoff efficiently. Using coal gangue to treat runoff was an effective way to reuse coal mining waste material as well as to deal with the gangue accumulation and stealing agriculture land issue.
Competing Interests
The authors declare that they have no competing interests.
Acknowledgments
The authors wish to thank the National Natural Science Foundation of China (41403090), the Foundation of Jiangsu Collaborative Innovation Center for Building Energy Saving and Construct Technology (SJXTY1507), and “the Fundamental Research Funds for the Central Universities” (2013QNB08).