Outdoor experiments with Lemnagibba (a duckweed species) grown in mini-ponds were conducted for several months during summer 1986. Duckweed was grown on two different types of wastes: (a) Digested sludge after an anaerobic phase of the settled fraction of domestic sewage mixed with the supernatant (experiment A); and (b) supernatant of domestic sewage at three different salinity levels defined by electrical conductivity (EC) (control, 4.0 dS/m and 6.6 dS/m) (experiment B). The results indicate that duckweed can grow well on a mixture of digested sludge and supernatant. Dry yield (experiment A) was in the range of 10 to 15 g/m2 per day with a protein content close to 30 percent. Effluent quality meets agricultural irrigation criteria. Duckweed growth on saline waste was mostly negatively affected when the electrical conductivity of the influent exceeded 4 dS/m.

A mathematical model of deep-bed filtration has been calibrated and verified based on experimental results. The experimental system, used for testing of the secondary treatment quality and the tertiary filtration phase, incorporates an SBR system followed by a filtration column. The turbidity of the incoming SBR effluent was in the range of 12 to 34 NTU. The bed grain size was in the range of 1.4 to 2.0 mm. The examined filtration velocities were 11, 15, 20 and 25 m/h. The filtration process is simulated by equations of balance and kinetics. The latter includes the attachment and detachment process, characterized by rate coefficients KA and KD, respectively. These coefficients , as well as the parameters of hydrodispersivity and effective porosity, are found on the basis of nonlinear optimization, using numerical solution of the model and the experimental breakthrough curves. The method demonstrates good agreement between experimental and simulated results.

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The project exploits the use of Artificial Neural Networks (ANN) to describe infiltration, water, and solute distribution in the soil during irrigation. It provides a method of simulating water and solute movement in the subsurface which, in principle, is different and has some advantages over the more common approach of numerical modeling of flow and transport equations. The five objectives were (i) Numerically develop a database for the prediction of water and solute distribution for irrigation; (ii) Develop predictive models using ANN; (iii) Develop an experimental (laboratory) database of water distribution with time; within a transparent flow cell by high resolution CCD video camera; (iv) Conduct field studies to provide basic data for developing and testing the ANN; and (v) Investigate the inclusion of water quality [salinity and organic matter (OM)] in an ANN model used for predicting infiltration and subsurface water distribution. A major accomplishment was the successful use of Moment Analysis (MA) to characterize “plumes of water” applied by various types of irrigation (including drip and gravity sources). The general idea is to describe the subsurface water patterns statistically in terms of only a few (often 3) parameters which can then be predicted by the ANN. It was shown that ellipses (in two dimensions) or ellipsoids (in three dimensions) can be depicted about the center of the plume. Any fraction of water added can be related to a ‘‘probability’’ curve relating the size of the ellipse (or ellipsoid) that contains that amount of water. The initial test of an ANN to predict the moments (and hence the water plume) was with numerically generated data for infiltration from surface and subsurface drip line and point sources in three contrasting soils. The underlying dataset consisted of 1,684,500 vectors (5 soils×5 discharge rates×3 initial conditions×1,123 nodes×20 print times) where each vector had eleven elements consisting of initial water content, hydraulic properties of the soil, flow rate, time and space coordinates. The output is an estimate of subsurface water distribution for essentially any soil property, initial condition or flow rate from a drip source. Following the formal development of the ANN, we have prepared a “user-friendly” version in a spreadsheet environment (in “Excel”). The input data are selected from appropriate values and the output is instantaneous resulting in a picture of the resulting water plume. The MA has also proven valuable, on its own merit, in the description of the flow in soil under laboratory conditions for both wettable and repellant soils. This includes non-Darcian flow examples and redistribution and well as infiltration. Field experiments were conducted in different agricultural fields and various water qualities in Israel. The obtained results will be the basis for the further ANN models development. Regions of high repellence were identified primarily under the canopy of various orchard crops, including citrus and persimmons. Also, increasing OM in the applied water lead to greater repellency. Major scientific implications are that the ANN offers an alternative to conventional flow and transport modeling and that MA is a powerful technique for describing the subsurface water distributions for normal (wettable) and repellant soil. Implications of the field measurements point to the special role of OM in affecting wettability, both from the irrigation water and from soil accumulation below canopies. Implications for agriculture are that a modified approach for drip system design should be adopted for open area crops and orchards, and taking into account the OM components both in the soil and in the applied waters.

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