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Treatment of high volumes of wastewater containing low concentrations of pollutants is becoming increasingly important as the discharge regulations become more stringent. Most of the past work has focused on the removal of higher concentrations of pollutants and on the more traditional and more expensive adsorbents/ion-exchange materials. This work has focused on the ability of low-cost adsorbents, as compared to the more traditional adsorbents, to remove from a high-volume waste stream, low concentrations of pollutants. The low-cost adsorbents investigated in this research include peanut hulls, kudzu, peat moss, municipal leaf compost, a shredded kenaf agrofiber, and a cotton textile waste. The pollutant removal efficiencies and capacities of these materials were compared with the removal efficiencies and abilities of the more traditional adsorbents: activated carbon, zeolite, bonechar, and a cation-exchange resin, as well as with the traditional wastewater filter medium, sand. Unless the sand is surface-modified or it develops a biofilm, it is not expected to contribute significantly to the removal of pollutants through adsorption and/or ion-exchange.

These low-cost materials have been examined in a series of isotherm and breakthrough experiments. The traditional isotherm experiments have focused on the adsorption capacity of the media for a single metal using a high concentration test water, while the breakthrough experiments have focused on the pollutant removal ability throughout the complete breakthrough curve for a multi-contaminant wastewater in which the pollutant concentrations were typically approximately 1 mg/L.

The results for the single isotherm experiments for copper have shown that the maximum removal capacity was for bonechar with a capacity of approximately 90 mg Cu/g media, followed by the cation-exchange resin. Most of the other media had removal capacities of less than 50 mg Cu/g media. Of the low-cost adsorbents, the peat, the compost, the kudzu, and the ammonia-removing zeolite had the greatest removal capacities, approximately 20 – 30 mg Cu/g media.

While this is a significant difference in capacity for the single metal between these materials, most waste streams do not contain only a single pollutant in its pure ionized form and they may not contain the large initial concentration of the metals that are used for traditional isotherm testing. For this reason, breakthrough testing of several media (activated carbon, zeolite, sand, compost, peat, agrofiber and cotton) was performed with a test water where the maximum concentration of any pollutant was 1 mg/L. The pollutants of interest were copper, iron, sulfate, nitrate, ammonia, and phosphate. Results of this testing for copper are shown in the graphs below. As the graphs indicate, pollutant removal capacity for copper even in a multi-component mixture and under low pH conditions, is significantly larger in the organic media, as opposed to the fibrous media and the traditional granular adsorbents: zeolite and activated carbon. These results indicate the robustness of the organic media to treat low concentrations of pollutants to an acceptable level (copper was not detected in the effluent of the columns until at least 0.5 g Cu/g peat and at least 1.0 mg Cu/g compost had been loaded on the column [Cu detection limit in solution of 0.1 μg/L]). The copper removal ability in the fibrous media (the cotton and the agrofiber) was not as high as in the organic media, however, it appears that the capacity of these two are comparable to that of activated carbon and zeolite, and they are significantly cheaper. Certainly, the results of the compost (a municipal leaf waste) and the cotton textile waste indicate a potential for reuse of these two waste materials in the treatment of low levels of pollutants in wastewater.

This work has been funded in part by the Water Environment Research Foundation (“Innovative Metals Removal” project).
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Document Type: Research Article

Publication date: 2000-01-01

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