lites possess a cation-exchange capability of about 2.25 meq g-1, and are able to exchange ammonium-N with sodium (Na) and potassium (K) ions (Mumpton, 1999). Theoretically, one gram of clinoptilolite can take in about 2.2 mg ammonium-N. This cation-exchange capability has been utilized effectively for terrestrial agriculture, where clinoptilolites are first saturated with ammonium-N and then incorporated into crop soils.
In this way they act as a slow-release fertilizer, with plants able to extract the sequestered ammonia from the clinoptilolite (Barbarick and Pirela, 1984; Lewis et al., 1984; Dwairi, 1998). Not only does clinoptilolite improve nitrogen fertilization efficiencies, it also reduces nitrate leaching by inhibiting the nitrification of ammonium to nitrate (Perrin et al., 1998). Most of the manure-ammonia sequestered in the zeolite is unavailable to nitrifying bacteria because of the small (4Ð5 angstrom) pore size of the crystal lattice structure (Mumpton, 1999). Furthermore, clinoptilolites are also used for animal waste management. Clinoptilolites are replacing clays in the cat litter industry, and are being used to create an odorless, nitrogen-rich compost from livestock manures.
The use of clinoptilolites in aquaculture has focused on ammonia removal for the aquarium industry and freshwater culture systems (Bower and Turner, 1982; Dryden and Weatherley, 1987). The research below examined an additional use of clinoptilolite for aquaculture analogous to terrestrial applications for agriculture and animal waste management: i.e., as a vehicle for ammonia absorption and subsequent fertilization to stimulate algal productivity.
Specifically, the objectives of the research described in this report were to:
1. Determine the relationship between total ammonia-N (TAN) absorption/saturation by clinoptilolite as a function of exposure time to fresh swine manure and liquified chicken manure,
2. Evaluate the release of TAN from ammonia-enriched clinoptilolite when used as a N fertilizer for stimulating algal production in an outdoor system,
3. Determine the ability of clinoptilolite to moderate TAN concentrations in an outdoor fertilized culture system, and
4. Evaluate the effectiveness of clinoptilolite for removing TAN from discharged pond water.
Methods and Materials
This study was conducted at the Asian Institute of Technology (AIT), Pathumthani, Thailand, within the Agriculture, Aquatic Systems and Engineering Program. There were a total of five experiments designed to achieve the above objectives. The crushed clinoptilolite (about 1Ð2 mm diameter) used in the study originated from Potos’, Mexico (supplied
by Geoexplorers International, Inc., Denver, Colorado), and had an exchangeable potassium:sodium ratio of about 8:1. Fresh chicken and swine manures were collected from broiler and pig houses of local farms. Manures were liquified by adding water followed by thorough mixing before each experiment. Making the manures more liquid facilitates the cation-exchange process between K and ammonium ions.
Experiment 1. The first experiment was a preliminary analysis of clinoptilolite's capacity to adsorb ammonia-N and/or urea, and to compare different analytical methods for estimating TAN in clinoptilolite. Fifty grams of clinoptilolite, which had been pre-washed five times with 200 ml deionized water and dried at 105¡C for two hours, were placed into each of three 1-l flasks. One flask then received 500 ml of a 2M ammonium chloride solution, the second flask received 500 ml of a 2M urea solution, and the third flask received 250 ml of the 2M ammonium chloride and 2M urea solutions. After immersion for four days, the clinoptilolite was removed from the solutions, washed five times with 200 ml deionized water, and dried overnight at 70¡C. Subsamples of about 1 g each were randomly taken from the semi-dried clinoptilolite removed from the three treatment solutions. Clinoptilolite subsamples were analyzed for TAN content directly, or after drying at 105¡C for two hours, using either Kjeldahl nitrogen analysis (Brenner and Mulvaney, 1982) or a phenate method (APHA, 1985) following ammonia-N extraction using 50 ml of 2M potassium chloride solution for two days.
Experiment 2. The second experiment used a 2 2 factorial design to test the effects of manure types and agitation on TAN absorption by clinoptilolite. The experiment was conducted in twelve 20-l plastic buckets, with three randomly selected buckets for each treatment. The four treatments were: 1) chicken manure slurry with agitation (CM-A), 2) chicken manure slurry without agitation (CM-NA), 3) swine manure with agitation (SM-A), and 4) swine manure without agitation (SM-NA). Each bucket received 7.5 kg manure and 7.5 l tap water, and was mixed thoroughly using a bamboo stick. Crushed clinoptilolite was placed in small-mesh nylon bags (16 meshes per inch), with about 1 kg clinoptilolite per bag. There was one bag per bucket, suspended in the manure by hanging it from the bucket handle. Bags in the agitation treatments were vertically hand-agitated for 30 seconds before and after each sampling. One clinoptilolite subsample of about 3 g was taken from each bag at 0, 0.25, 0.5, 1, 2, 4, 8, 24, 48, 96, and 168 hours after the bags were first immersed into the buckets, and analyzed for TAN content. Samples of liquified manures taken at the beginning and end of the experiment were also analyzed for TAN.
Experiment 3. The third experiment evaluated the efficiency of TAN release from clinoptilolite enriched with ammonia,