Marcelo Juanico

Design, operation and performance of stabilization reservoirs for wastewater irrigation in Israel

Abstract Stabilization reservoirs are used for the seasonal storage and treatment of wastewater for irrigation. These reservoirs are not steady-state flow reactors, but rather accumulative batch ones with a relatively abrupt discharge. A new parameter, the percentage of fresh effluents within the reservoir (PFE) is proposed as a tool to analyze the age distribution of effluents in this kind of reactor. The equations to calculate the mean residence time (MRT) and the surface organic loading are also provided. The relatively small fraction of fresh effluents represented by PFE and not the whole age distribution of the effluents (MRT) determines the removal percentages of COD and BOD in the reservoir and the quality of the effluents released for irrigation. The effect of environmental parameters such as water temperature and solar radiation are overridden by the operational parameters (PFE). In steady-state flow reactors MRT can substitute PFE to evaluate the reactor performance because the ratio PFE/MRT is constant in this particular case. A value of 30–40 kg BOD/ha/day is recommended as the maximum allowable surface organic loading of stabilization reservoirs. The seasonal storage of wastewater in reservoirs reduces BOD, COD, TSS and detergents by 50–80%, and total coliforms by 90%, in terms of annual means. The quality of the effluents is maximal at the beginning of the irrigation season when the reservoir is full of old effluents, but sharply deteriorates when water level drops and new wastewater is pumped into the reservoir. Design and operational alternatives to overcome this problem can assure removals of at least I order of magnitude for chemical components, and of at least 3–4 orders of magnitude for total coliforms. These alternatives are based on a change from seasonal to multi-seasonal storage of wastewater, and/or a change from single reservoir to two or more reservoirs supplying effluents of different quality.

COLIFORM REMOVAL IN A STABILIZATION RESERVOIR FOR WASTEWATER IRRIGATION IN ISRAEL

The removal of faecal and total coliforms is studied in a reservoir where wastewater is stored during the rainy winter to be used for irrigation during the dry summer. The operational regime of the reservoir is irregular, changing between non-steady-state flow and batch. The ranges of the reservoirs key parameters are: inflow faecal coliforms, IOh-101/100 cm3; water level, 2.3-5.5 m; water temperature, 10-3OCC; pH, 6.9-8.6; mean hydraulic residence time, 50-180 days; surface organic loading, &340 kg CODlhaIday. Coliform removal is high in the epilimnion where high pH values occur due to algal activity, and low in the hypolimnion where pH values are much lower. When the reservoir is operated as a flow reactor, coliform removal is determined mainly by the percentage of fresh effluents within the reservoir (PFE) and not by the mean residence time of the effluents (MRT). The coliform removal percentage is one to two orders of magnitude when the reservoir is operated as a flow reactor, but it can reach more than five orders of magnitude when operated as a batch reactor. A proper combination of flow operation during winter and batch operation during summer can assure a coliform removal of at least five orders of magnitude during the whole irrigation season. Coliform removal can also be improved by vertical mixing of the water column, the use of a horizontal diffuser device in the outlet, and the design of elongated reservoirs. Key words-stabilization reservoirs, wastewater storage. wastewater treatment, wastewater irrigation, faecal coliforms, unsteady-state flow reactor, batch reactor

Salt Enrichment of Municipal Sewage: New Prevention Approaches in Israel

Wastewater irrigation is an environmentally sound wastewater disposal practice, but sewage is more saline than the supplied fresh water and the salts are recycled together with the water. Salts have negative environmental effects on crops, soils, and groundwater. There are no inexpensive ways to remove the salts once they enter sewage, and the prevention of sewage salt enrichment is the most immediately available solution. The body of initiatives presently structured by the Ministry of the Environment of Israel are herein described, with the aim to contribute to the search for a long-term solution of salinity problems in arid countries. The new initiatives are based on: (1) search for new technologies to reduce salt consumption and discharge into sewage; (2) different technologies to cope with different situations; (3) raising the awareness of the public and industry on the environmental implications of salinity pollution; and (4) an elastic legal approach expressed through new state-of-the-art regulations. The main contributor to the salinity of sewage in Israel is the watersoftening process followed by the meat koshering process. Some of the adopted technical solutions are: the discharge of the brine into the sea, the substitution of sodium by potassium salts in the ion-exchangers, the construction of centralized systems for the supply of soft water in industrial areas, the precipitation of Ca and Mg in the effluents from ion-exchangers and recycling of the NaCI solution, a reduction of the discharge of salts by the meat koshering process, and new membrane technology for salt recovery.

Simulation model of wastewater stabilization reservoirs

Abstract Stabilization reservoirs are hypertrophic aquatic systems functioning under non-steady-state conditions. The use of stabilization reservoirs is especially suitable for warm countries suffering from water shortage, where regulation between wastewater production and effluent utilization is needed. Stabilization reservoirs can significantly improve effluent quality; however, only few models have been developed to date. Today, with growing demand for high quality effluent, better understanding of the processes occurring in the reservoirs is needed. This paper describes the development of a mechanistic simulation model that integrates knowledge from the fields of wastewater treatment and limnology. The model has five quality variables in the waterbody and two in the sediment. It was calibrated and verified on three stabilization reservoirs in Israel and exhibited good agreement with observations. Different design and operation alternatives were studied, and some are discussed in this paper. The prediction ability of the model turns it into a useful research and design tool for studying the influence of various design and operation alternatives on the reservoirs’ efficiency as wastewater treatment units.

Removal of trace metals from wastewater during long-term storage in seasonal reservoirs

The removal of five metals (Cu, Zn, Cr, Pb, Al) was studied in two reservoirs in series used for the seasonal storage of wastewater effluents for irrigation. The evaluation was made by two methods: (1) an anual budget which includes inputs and outputs and. (2) sediment traps. The concentrations of metals were reduced between 20 and 75%, to the base level found in unpolluted groundwater in the region. The amount of Pb was reduced in 5%, Cu in 10%, Al in 30%, Cr in 50%, and Zn in 90%. Sedimentation has an irregular pattern due to the effect of wind induced longshore and rip-currents. The release of bottom sediments in the outflow means a direct release of trace metals and other settling pollutants and clogging particles. It is recommended to take the effluents for irrigation from the uppermost water layer, to avoid strong outflow rates which may drag out part of the sediments by hydraulic turbulence, and to locate the outlet away from the dominant wind axis. The main tools to improve the removal of trace metals in seasonal reservoirs are not the control of the age distribution of the effluents and/or the loading of the reservoirs, but the proper location, design and flow rate of the outlet.

Alternative schemes for municipal sewage treatment and disposal in industrialized countries: Israel as a case study

Abstract The selection of appropriate technology for municipal sewage treatment and disposal requires not only a proper characterization of modern municipal sewage but also the analysis of agriculture-generated pollution. Modern municipal sewage contains a wide spectrum of xenobiotic pollutants with negligible oxygen demand, and BOD is no longer the descriptor of effluent quality. Intensive sewage treatment systems (such as activated sludge) successfully remove BOD but fail to remove refractory pollutants and pathogens. A proper combination of semi-intensive reactors (such as aerated lagoons) for the partial removal of BOD, with extensive reactors (such as wastewater reservoirs) for the removal of refractory pollutants and pathogens, will release effluents of much better quality than other alternative schemes, at lower costs. Wastewater irrigation fails to assure nutrient recycling through agriculture products if not accompanied by a change in fertilization practices. The present system of subsidies to agriculture in industrialized countries promotes the over-application of fertilizers and biocides, and the over-production of agriculture commodities. The incorporation of the rural sector to the sewage treatment system of the urban sector will substitute the present conflict of interests between the two sectors by a partnership with strong environmental and economic bases.

Effect of effluent addition to a freshwater reservoir on the filter clogging capacity of irrigation water

Abstract This paper deals with the effect of the addition of effluents to a shallow freshwater reservoir used for irrigation, on the clogging capacity of the water. The clogging capacity was estimated with an instrument that measures the increasing differential pressure needed to maintain a constant flow of water through a 30 μm screen filter. The dependence of the clogging capacity on plankton composition and suspended solids concentration was studied by means of multiple regression analysis, on four different arrangements of the matrix of data. The addition of effluents raised the clogging capacity sharply and quickly. The phenomenon was primarily due to an increase in the number of large algae and zooplankton species. These large species partially substituted for the small ones which were dominant before the entry of effluents. The concentration of suspended solids also affected the clogging capacity, but to a much lower extent. A relationship between the clogging capacity and the total number of plankton organisms was not found. The addition of plankton filter-feeding fish to the reservoir is recommended.

Variability of effluent quality in a multi-step complex for wastewater treatment and storage

The present paper deals with the variability of efluent quality in a complex for wastewater treatment and storage. The complex is made up of several steps: a treatment plant followed by a two-cell stabilization reservoir and an operational reservoir in series. The generally held notion that wastewater treatment units reduce inflow quality variability stem from the wrong use of standard deviation to compare data of different magnitude. The standard deviation is a statistic that describes the variability of data in absolute terms. It is not appropriate to compare outflow and inflow quality variability in a treatment plant, since outflow quality values are usually several times lower than inflow ones. The same problem arises when comparing different parameters (e.g. the variability of pH with the variability of BOD). In these cases it is necessary to describe the variability of data in relative terms. The coefficient of variation (CV) is used in this work to describe the variability of each single quality parameter at each step of the Kishon complex. There are conspicuous differences in variability between the wastewater quality parameters. These differences can help for a better selection of parameters for both monitoring and modelling purposes, as well as for determination of differential sampling frequencies in monitoring programs. The different steps of the treatment complex hardly differ in the variability of effluent quality as a whole, expressed as the average CV of all parameters in each step. Wastewater quality variability is only partially transmitted along the complex, but local born disturbance maintains the total amount of variability at each step almost unchanged. Control and reduction of variability at one step of the complex will not significantly affect the amount of variability in the subsequent steps.

Plankton community changes due to the addition of treated effluents to a freshwater reservoir used for drip irrigation

Abstract The present paper defines the structure and dynamics of the planktonic populations before and after the addition of reclaimed effluents to an operational irrigation reservoir. The analysis of the effects of the inflow of the effluents on the parameters that characterize the planktonic populations may serve to determine the means that have to be taken to improve the quality of the water used for drip irrigation. The planktonic communities in the reservoir were defined by factor analysis. The input of effluents led to a change from phyto- and zooplankton communities dominated by small species, to communities dominated by large species (greater than 200 μm). This change was characterized by an increase in biomass without an increase in the total number of algae. The dominating algae were species of Cyanophyta which responded to the input of N compounds rather than to the increase in phosphate concentration. Laboratory enrichment experiments support the idea that the limiting factor was the N compounds.

The use of non-conservative parameters to trace wastewater effluents in water bodies

Abstract This paper describes an alternative method to label wastewater effluent entering water bodies when “classic” tracers (artificial tracers and conservative parameters of the water masses) cannot be used. The method is based on the simultaneous use of several non-conservative effluent quality parameters (e.g. electrical conductivity, detergents, TDS, PO 4 , alkalinity, Na, Kjeldahl, NH 4 and NO 2 ). The simultaneous use of several parameters enables to smooth out the high variability of single non-conservative parameters disclosing their common trend. The obtained estimates are not quantitative but can be expressed in an ordinal scale. The performance of the new multi-tracer method is tested in a case study to estimate the relative amount of effluent in the outflow of an operational reservoir which receives freshwater and sporadic inputs of treated wastewater. The multi-tracer method disclosed poor mixing conditions between freshwater and effluents within the reservoir, plug flow-like movement of the effluent pulses with a delay of 1–3 weeks between an in-pulse and its corresponding out-pulse, and the existence of dead spaces in the reservoir.