Malka Kochba

Water content, organic carbon and dry bulk density in flooded sediments

Abstract Several basic properties of pond bottom soil are shown to be related, a relation that enable to evaluate pond bottom soil characteristics through the determination of one parameter (e.g. soil moisture). In addition, these relationships give some insight into the properties of flooded sediments. Unlike terrestrial soils, made of gas, liquid and solid phases, flooded sediments are made practically of only two phases, liquid and solid. Since all voids are filled with water, it is possible to evaluate soil porosity and bulk density, directly from the moisture content of the soil, a property easily determined. The correlation between bulk density and organic matter was tested in six different systems (n=868), including rivers and fish pond sediments in Israel, fish pond sediments in Alabama, USA, and Abbassa, Egypt, lake sediments in New Zealand, alpine lake sediments in Colorado, USA, and sea floor sediments from the Northwest African continental slope. Sediment bulk density was inversely related to the organic carbon concentration. The regression for all the data points was: Bulk density ( g/cm 3 )=1.776−0.363 Log e OC (R 2 =0.70) where OC is the organic carbon concentration (mg/g). The relationship between sediment moisture, bulk density and organic carbon described here can be used as a simple means to estimate the organic content and bulk density of flooded mineral soils by a simple determination of a sediment water content.

Studies on slow release fertilizers: I. Effects of temperature, soil moisture, and water vapor pressure.

Using first-order kinetics we describe the release of nutrients by coated slow-release fertilizer (SRF). Plotting the logarithm of the concentration of intact fertilizer in the soil [log(Q0 - Qt), where Qt, is the amount applied and Qt, is the amount released at time t] versus the time yielded a straight line, as predicted. The rate constants of SRF release at different temperatures are linearly related to the water vapor pressure: K = A · Pw + B where Pw is the vapor pressure and A and B are constants. We conclude that the rate-determining step in the nutrient release out of SRF is the migration of vapor from the soil into the fertilizer granule. The very mild effect of soil moisture on the rate of nutrient release is consistent with the proposed mechanism. We discuss the possibility of predicting nutrient release from SRF using the derived relationships.

Stability Indexes For Municipal Solid Waste Compost

Compost was prepared from the organic fraction of the municipal solid waste stream, using a windrow process. Stability was defined using rather simple tests. The pH was acidic at the beginning and stabilized near a neutral range. Electrical conductivity (EC) dropped and stabilized near a value of approximately 50 percent of the initial reading. The drop in EC was not due to leaching but to decomposition of organic acids. Another sensitive index was NH4 concentration. It decreased sharply from initial levels of a few hundred ppm to a stable value of about 50 ppm. The stability point as determined by simple chemical analyses of the aqueous extract of the compost correlated well with the decrease of the organic matter decomposition rate.

Rates of organic carbon and nitrogen degradation in intensive fish ponds

Abstract Water quality in intensive aquaculture systems is to a large extent controlled by the microbial biodegradation of organic residues. The ability to simulate processes in such systems depends on the availability of data on the rates of these processes. The first order kinetic rate constants for both organic carbon and organic nitrogen degradation in fish ponds were evaluated. The rate constants were computed by either relating the measured rate of disappearance of the substrate concentration or by the comparison of the measured with a theoretically derived evolution pattern of organic carbon or nitrogen concentrations in model ponds. The organic carbon degradation rate constant was found to be 0.15/day. The organic nitrogen degradation rate constant was expected, theoretically to be about 0.06/day and was found experimentally to be in the range of 0.05–0.09/day. These values seem to be reasonable approximations for constantly aerated-mixed ponds, at a temperature range of 20–30 °C. Organic matter previously metabolized in anoxic sites at the pond (e.g. resuspended sediments), has a degradation rate of ca. 0.6/day, and can thus consume large amounts of oxygen in the water body.

Modeling of nitrogen transformation in intensively aerated fish ponds

Abstract A model describing the nitrogen sub-system in a completely mixed and aerated pond is proposed. Inputs of nitrogen include feed and influent water; outputs of nitrogen include uptake by fish, removal of sediment from the pond and discharge water. Internal transformations between the inorganic and organic pools are also computed. The organic nitrogen that is introduced with the feed is mineralized through either ammonia excretion by fish or the microbial degradation of organic nitrogen. The opposite process—immobilization of nitrogen—occurs through algal nitrogen uptake or by microbial protein synthesis. Computed results may enable the design of an optimal water exchange rate. The simulation of ponds fed with different feed compositions and rates, having variable water exchange regimes, gave results close to the measured ones.

Combined intensive-extensive (CIE) pond system A: inorganic nitrogen transformations

Abstract Combined intensive-extensive (CIE) pond system composed of four 500-m 3 intensive ponds and a 1.4-ha lagoon was studied. Water was circulated between the intensive and extensive components. The average hydraulic residence time in the intensive ponds was 5 h. The role of nitrification was studied in the CIE system. It was shown that the nitrifying bacteria are not active in the system even though the conditions for nitrification seem favorable: the substrate for nitrification, ammonia, was always present and a high oxygen level was found in the intensive ponds. Nitrification started only following a 24-h lag period and progressed exponentially, in samples taken from the ponds and incubated in the laboratory with continual shaking. It was concluded that, due to the rapid flushing of the system, nitrifying bacteria are not able to adjust to the optimal conditions for nitrification existing in the intensive ponds. Efficient nitrification in the intensive ponds was achieved by increasing the hydraulic residence time in the ponds, as flushing rate was slowed.

Studies on slow-release fertilizers: II. A method for evaluation of nutrient release rate from slow-releasing fertilizers.

A method of evaluation of nutrient release from membrane-coated slow-release fertilizers is presented. The method is based on the gravimetric measurement of water-vapor uptake by individual fertilizer granules placed in a saturated water vapor chamber. The nutrient release from such fertilizer consists of two stages. In the first stage, water vapor infiltrates into the granule and condenses on the soluble fertilizer salt, leading to the development of pressure within the particle. The elevated pressure leads to swelling of the granule and the outward leakage of the fertilizer solution. The method yields results characterizing both the average rate of nutrient release and the release rate distribution among the population of fertilizer granules. The results are consistent with measurements of nutrient release rates in soil-fertilizer mixtures.

Effects of manuring rate on ecology and fish performance in polyculture ponds

Abstract The present study was designed to quantify the effect of manure application on fish performance and on the ecology of the ponds. Ponds stocked with common carp, tilapia hybrids, silver carp and grass carp received dry chicken manure as the only nutritional input, at three different rates: the standard level used at Dor (50 kg dry matter ha −1 day −1 , increasing by 25 kg ha −1 day −1 every 2 weeks up to 175 kg ha −1 day −1 , half of it, and twice the standard. Ecological data included water and sediment parameters, and were analysed through factor analysis and ANOVA. Organic loading increased in two directions, time and treatment. The main sources of variability in the system were related to time. The low effect of treatment was shown in both fish performance and ecological parameters. Of the fish parameters tested, only total yield and common carp growth rate and vield increased with manuring rate. Water quality variability was mainly related to photosynthesis-decomposition balance and algal and bacterial action to metabolize nitrogen, processes which were affected by time and not by manuring rate. A third source of variability in the water column, the respiration of the system, was lower in the treatment with the lower manuring rate. Manuring rate and time strongly affected ecological processes in the sediments: organic loading and anaerobic conditions increased and heterotrophic activity decreased with time and manuring rate, while microbial metabolization of nitrogen decreased with time and increased with manuring rate. The lack of treatment effect on growth and yield of all fish species, except common carp, seems to be related to this difference in the effect of manure level on water and sediment: while common carp feeds on the bottom and is more dependent on feed supplied than the other fish present in the pond, silver carp feeds on phytoplankton in the water body, and tilapia hybrids also favour natural foods of photosynthetic origin.

Development and evaluation of a biofilter for turbid and nitrogen rich irrigation water

Abstract The biofilter system proposed and tested here, for upgrading irrigation water, is based upon the use of a carbonaceous material, such as wheat straw, as a substrate for microbial activity. Microorganisms degrading a carbon-rich and nitrogen-poor substrate are expected to take up nitrogen from the water. When wastewater flows along a column of the carbonaceous substrate, a sequence of nitrification and denitrification is also possible. Moreover, the biofilter may “trap” phosphorus, suspended matter and possibly soluble organic matter. Each biofilter (a 1 m 3 PVC tank containing 50 kg of wheat straw) was fed by water from an oxidation pond at a rate of 60–65 1 h −1 . The biofilter system performed with no clogging or other hydraulic problems for a period of 63 days. The capacity of the filter was at least 2 m 3 water for each kg of straw. The biofilter removed 50% of the ammonium from the input water, 65% of the suspended matter and 75% of the algal biomass. In addition, the leachates from the biofilter were more uniform than the raw pond water, the composition of which fluctuated within a wide range. Besides its smooth operation, the raw straw was enriched with protein during the operation of the filter. The initial protein content of the straw (about 3%) rising to 12–15% by the end of the experiment. It is anticipated that the spent straw may be used as a manure, or, probably following silage, as a valuable feed material.

Nitrification pattern in a fluctuating anaerobic-aerobic pond environment

Abstract Nitrification does not occur in conventional fish ponds or in oxidation ponds. Yet, intensive nitrification occurs in continually aerated and mixed fish ponds and in activated sludge systems. In a combined fish pond system, water from a conventional pond is pumped through a continually aerated and mixed pond, with a 5 h average hydraulic residence time. Unlike other aerated ponds, nitrification did not occur in this case. The reasons for nitrification inhibition were studied in laboratory and field experiments. Inhibited nitrification was not due to any factor associated with water composition and persisted even when the water was replaced. In addition, it was not limited by a lack of inoculum. Nitrification in a laboratory assay started immediately in samples taken from a continually aerated pond, while it started only following a 24–48 h lag period in water sampled from a conventional pond or from the combined pond system. Nitrifying bacteria have to adapt to the partial anoxic conditions in the conventional pond. It is assumed that the lag period is needed by the reverse process, adaptation to oxic conditions. The ecological and practical implications of this phenomenon are discussed. The lag period is needed when nitrifiers are transferred from anoxic to oxic conditions as a protective mechanism to ensure that nitrification will take place only if continuous or long-term oxic conditions prevail.