G. Shelef

Some biochemical aspects of the anaerobic degradation of dairy wastewater

Abstract Low rate of anaerobic degradation together with inhibition problems caused by components such as milk fat and proteins were found to be reasons for restricted activity of high-rate anaerobic reactors operated with dairy effluent. The present research was aimed to investigate the influence of some relevant compounds, such as casein and milk fat and their degradation compounds, on process efficiency. Methanogenic activity and ATP content of the sludge were used as major follow up criteria for evaluating the influence of the tested compounds on process efficiency. It was found that casein was not degraded by anaerobic cultures which were not pre-acclimated for this compound. On the other hand, cultures acclimated to casein, utilized it very efficiently. Amino acids typical for casein degradation were also used efficiently with no inhibitory effects under the test conditions and with no need for culture pre-acclimatization. Milk fat was found to be a major cause for inhibition of methanogenic activity. It was found to have an immediate influence on reducing gas production rate in reactors to which it was added. Milk fat was also found to have long term effects: sludge pre-exposed to milk fat exhibited reduced methanogenic activity when tested in medium free of milk fat. Milk fat also reduced the ATP concentration in the sludge, indicating reduction of its total physiological activity. Oleic acid, which is a major derivative of milk fat hydrolysis was found to have inhibitory effects on methane production and on ATP concentration. According to the results of the present research, it would be advisable to treat dairy effluents by anaerobic digestion only after reduction of the milk fat concentration below 100 mg/L, and after careful acclimatization of the digester culture to casein.

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.

Microbial degradation of aromatic and polyaromatic toxic compounds adsorbed on powdered activated carbon

Abstract The microbial degradation of phenol (300–1300 mg l −1 ), p -nitrophenol (50–500 mg l −1 ), and phenanthrene (50–300 mg l −1 ) adsorbed on powdered activated carbon (PAC) was studied. The combination of physical sorption and biological degradation on PAC, which serves as adsorbent carrier, was compared with the degradation performance of suspended cells and cultures attached to sand, which serves as an example of an inert support. Almost similar profiles of degradation were obtained in the cultures with PAC for the three compounds studied, over the entire concentration range. However, at the higher concentrations, degradation was dramatically inhibited, or even ceased completely, in suspended or sand-attached cultures, even though specialized mixed bacterial cultures adapted to high toxicant concentrations were used in each case. Degradation with PAC assumes an intrinsic relationship between the activated carbon and bacteria in the same environment, thus regenerating the surface of the adsorbent/ carrier as diffusion and degradation proceed. The adsorbed material desorbs, diffuses out of the carbon and can then be metabolized. Our results highlight the applicability of activated carbon, in either powdered or granular form, to achieve a steady-state operation in continuous process, for the treatment of toxic chemicals, even with specialized bacteria.

Effect of oxidants on microalgal flocculation

Abstract The effects of chlorine, ozone and chlorine dioxide on Scenedesmus sp. cultures were studied. Algal cell viability and chlorophyll concentration decreased, and the concentration of dissolved organic substances increased with increasing applied oxidant concentration. Pretreatment with chlorine dioxide (1, 3 or 5 mg l −1 ) or ozone (2.6, 4.6 or 8.1 mg l −1 ) on algal cultures enhanced algal flocculation with alum, while prechlorination with 10 or 20 mg l −1 increased the required dosage of alum by 15%. Scanning electron micrographs of oxidized cells revealed drastically adverse effects upon the cell surface architecture: in addition to the oxidation of noncellular organic materials, the oxidants damaged both cell surface structures and intracellular components. A model explaining the effects of the different oxidants on microalgal flocculation is suggested.

Operation of high-rate oxidation ponds: theory and experiments

Abstract Optimal operation of high rate oxidation ponds depends mainly on the climatic conditions of the ponds location. The major factors affecting pond performance are solar radiation and water temperature, the former determines mainly maximal algal productivity while the latter determines optimal retention time operation. Pond dimensions, namely area and depth, are the only true independent variables which can be manipulated to produce optimal retention time in year-round operation. In the tropical regions a constant retention time is most adequate for optimal operation as water temperature is fairly constant year-round and a constant area and depth strategy can be adopted. In moderate climates seasonally variable retention time is preferred and it was found to be best economically achieved by varying pond depth at constant area. Another plausible strategy with possible economic advantages is a combination of dual function ponds operating solely for wastewater treatment during winter while some are converted into fish-rearing ponds during summer.

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

Utilization of municipal solid wastes (MSW) for alcohol production

Abstract Treatment of Municipal Solid Wastes (MSW) yielding high-value products, in our case ethanol, energy and enriched plant growth media, are the objectives of this R & D program. The process includes resource recovery and combined treatment of MWS based on dilute acid hydrolysis and alcohol fermentation. The hydrolysis experiments were carried out at the Technion in a batch reactor and at the New York University in an extruder type reactor. It was found that the optimal conditions for the acid hydrolysis are: temperature of 230–235°C; pressure of 30–32 atm., pH value of about 0·50 and reaction time of 8–15 s. Under these conditions glucose yields of about 60% can be achieved. Methods to overcome toxicity problems while achieving high ethanol yields (better than 85%) in high substrate concentrations ( TS = 25%) were developed, as well as techniques for byproducts utilization.

Coprecipitation of microalgal biomass with calcium and phosphate ions

Abstract Algal cultures which tended to flocculate under alkaline conditions were investigated in order to define the flocculating agent. Under the electron microscope, cells appeared to be agglomerated by inorganic “amorphous” precipitates or rod shaped microcrystals. The use of an energy dispersive X-ray analyser showed that the agglomerating substance consisted of calcium and phosphorus and their atomic ratios varied between 1.07 and 1.34. The experiments suggest that in autoflocculation involving chemical coprecipitation with biomass, calcium phosphate constitutes the major binding agent. The Ca:P ratio in the precipitated calcium phosphate is greatly increased by raising alkaline conditions or increasing precipitation period.

The effect of the neutralizing capacity of cellulosic materials on the kinetics of cellulose dilute acid hydrolysis

Abstract The production of ethanol has become a new field of investigation for the satisfactory and economical treatment of municipal solid waste (MSW). Since cellulose is a major component of MSW it may be treated as a resource for fuel, chemical and energy recovery. The key, and the difficult, engineering point of this process is the cellulose hydrolysis step in which the chemically resistant cellulose is converted to sugar (glucose) in the presence of acid as a catalyst. The later fermentation to ethanol by yeast should not be a problem. One of the main problems encountered in determining cellulose acid hydrolysis kinetic parameters is the effect of the neutralization capacity of cellulosic materials on the effective acid concentration. This paper shows how important and influential can be the neutralization capacity of cellulosic materials (sawdust and MSW) and teh effect is subsequently quantified. The use of the pH as a measure of the real effective H 3 O + concentration is strongly recommended.

COMBINED ALGAE PRODUCTION - WASTEWATER TREATMENT AND RECLAMATION SYSTEMS

Abstract Treatment of municipal wastewater in High Rate ponds has been extensively studied in a multitude of outdoor pond units. The ponds are 35 to 50 cm deep with folding channels and are mixed and aerated by a rotor cage aerator. The suspended biomass is separated by flocculation and flotation yielding high quality effluent and algal “froth” containing between 5 to 10 percent solids to be further dewatered and drum dried. Average production of photoautotrophic algae reached 22gr m−2day−1 which constitute about 5.8 percent conversion efficiency of the photosynthetically available light. The photosynthetic oxygen supply reached over 35 gr m−2day−1 which constitute over two thirds of the oxygen demand for the aerobic degradation of the waste matter. Predominant algal species such as Scenedesmus dimorphus , Micractinium quadrisetum , Phytoconis sp . and Oocystis solitaria varied seasonally in the pond without any significant change in growth and productivity. Dried algae containing up to 4 percent aluminium (flocculant residue) were fed to carps ( Cyprinus carpio ) and to St. Peters fish ( Tilapia galilea ) where 85 percent of the fish-meal portion of commercial diet (usually 15 percent of diet) was replaced by 30 percent algae in the feed (equal protein level). Fish weight gain and health were equal if not improved by this algae containing diet. The algae also served for feeding of young chicks (1–8 weeks) with no mal-effects where algae (containing aluminium) replaced 25 percent of the proteins in the diet. The economy of the overall system is based on the value of wastewater treatment, the added value of the final effluent high quality rendering its reuse for agricultural irrigation and the value of the harvested algae as a proteinaceous feed. Once the need exists for all three values, the system is highly competitive vs. any other wastewater treatment process where the proper climatic conditions and land availability exist.