Michal Green

Ammonium removal using ion exchange and biological regeneration

A new concept for ammonium removal from secondary effluent by zeolite followed by bioregeneration has been studied. In contrast to other studies of hybrid biological-ion exchange multireactor Systems, the proposed process uses the ion exchange material, zeolite, as a carrier for the nitrifying biomass. Therefore, the entire process is carried out in a single reactor. Since all the ammonium from the original effluent is concentrated in the zeolite and released gradually during regeneration, nitrification is carried out in a small volume reactor in an almost batch mode where optimal conditions for nitrification can easily be maintained. Moreover, the conversion of ammonium cations to nitrate anions allows for regenerate recycle, where the amount of chemicals added for desorption is reduced to the amount of sodium bicarbonate added as a buffer for nitrification. As a result, operational costs and production of large volumes of brine are minimized. To achieve sufficient NH4+ concentration in the solution to allow for high rate nitrification, the cation-rich regenerant solution (or part of it) is reused from one cycle to the next. A theoretical model including ion exchange and bioregeneration modes, indicates that the total cation concentration and each cation in the recycled regenerant should reach constant values after several cycles of adsorption-regeneration and remain constant as long as the influent characteristics and operation conditions stay similar. Experiments results verified the predicted values

High-Rate Nitrification at Low pH in Suspended- and Attached-Biomass Reactors

ABSTRACT This article reports on high-rate nitrification at low pH in biofilm and suspended-biomass reactors by known chemolithotrophic bacteria. In the biofilm reactor, at low pH (4.3 ± 0.1) and low bulk ammonium concentrations (9.3 ± 3.3 mg · liter−1), a very high nitrification rate of 5.6 g of N oxidized · liter−1 · day−1 was achieved. The specific nitrification rate (0.55 g of N · g of biomass−1 · day−1) was similar to values reported for nitrifying reactors at optimal pH. In the suspended-biomass reactor, the average pH was significantly lower than that in the biofilm reactor (pH 3.8 ± 0.3), and values as low as pH 3.2 were found. In addition, measurements in the suspended-biomass reactor, using isotope-labeled ammonium (15N), showed that in spite of the very low pH, biomass growth occurred with a yield of 0.1 g of biomass · g of N oxidized−1. Fluorescence in situ hybridization using existing rRNA-targeted oligonucleotide probes showed that the nitrifying bacteria were from the monophyletic genus Nitrosomonas, suggesting that autotrophic nitrification at low pH is more widespread than previously thought. The results presented in this paper clearly show that autotrophic nitrifying bacteria have the ability to nitrify at a high rate at low pH and in the presence of only a negligible free ammonia concentration, suggesting the presence of an efficient ammonium uptake system and the means to cope with low pH.

Enhancing nitrification in vertical flow constructed wetland utilizing a passive air pump

Abstract Nitrification of simulated secondary effluent solution using a variant of the vertical flow bed constructed wetland was studied. In this system oxygen required for the nitrification process is supplied by a passive air pump. The passive air pump is based on a fill and draw cycle, where oxygen depleted air is removed from the system while fresh air is introduced. Each volume of effluent drained is displaced by an equal volume of fresh air. Spatial and temporal oxygen distribution in the system as a function of drained effluent volume was investigated. Experimental results of nitrification and the corresponding oxygen consumption show good agreement with theoretical calculations based on physico–chemical considerations. Observations show that while oxygen distribution within the media was found to be non-uniform at the beginning of each cycle, it approached more uniform distribution with time. The latter resulted mainly from diffusion of oxygen in the gaseous phase.

Nitrification in a Biofilm at Low pH Values: Role of In Situ Microenvironments and Acid Tolerance

ABSTRACT The sensitivity of nitrifying bacteria to acidic conditions is a well-known phenomenon and generally attributed to the lack and/or toxicity of substrates (NH3 and HNO2) with decreasing pHs. In contrast, we observed strong nitrification at a pH around 4 in biofilms grown on chalk particles and investigated the following hypotheses: the presence of less acidic microenvironments and/or the existence of acid-tolerant nitrifiers. Microelectrode measurements (in situ and under various experimental conditions) showed no evidence of a neutral microenvironment, either within the highly active biofilm colonizing the chalk surface or within a control biofilm grown on a nonbuffering (i.e., sintered glass) surface under acidic pH. A 16S rRNA approach (clone libraries and fluorescence in situ hybridizations) did not reveal uncommon nitrifying (potentially acid-tolerant) strains. Instead, we found a strongly acidic microenvironment, evidence for a clear adaptation to the low pH in situ, and the presence of nitrifying populations related to subgroups with low Kms for ammonia (Nitrosopira spp., Nitrosomonas oligotropha, and Nitrospira spp.). Acid-consuming (chalk dissolution) and acid-producing (ammonia oxidation) processes are equilibrated on a low-pH steady state that is controlled by mass transfer limitation through the biofilm. Strong affinity to ammonia and possibly the expression of additional functions, e.g., ammonium transporters, are adaptations that allow nitrifiers to cope with acidic conditions in biofilms and other habitats.

Biodegradation kinetics of hydrocarbons in soil during land treatment of oily sludge

This study focuses on the processes influencing hydrocarbon residue persistence in soil, following land treatment of refinery oily sludge. Treating sludge applied to soil resulted in 70% to 90% degradation of total petroleum hydrocarbon (TPH) during 2 months, regardless of their initial concentrations (9 to 60 g/kg soil). Kinetic analyses performed on TPH degradation, in laboratory and field systems, revealed a degradation pattern characterized by two consecutive first-order kinetics reactions in all experimental settings. The first stage lasted about 3 weeks and was characterized by a temperature dependent rate constant of 0.047 day−1 at 24°C. That value was comparable to the rate constant obtained when combining the individual rate constants of the saturated, aromatic, asphaltene and polar fractions. The subsequent slower stage rate constant was 0.012 day−1, insensitive to temperature and to hydrocarbon composition. The transition between the two stages (about 21 days) was independent of the experimental temperature and the biodegradation extent during the first stage. It was concluded that the extent of residual accumulation in the soil was determined by the biodegradation efficiency during the first three weeks of treatment when biological processes dominated. During the following period, abiotic processes leading to reduced bioavailability of the TPH were limiting the degradation rate. Practically, as the first few weeks of treatment determine its efficiency, efforts to enhance the biological activity should be directed to that period.

Constructed wetlands for river reclamation: Experimental design, start-up and preliminary results

Abstract The use of constructed wetlands for the treatment of secondary effluents, to allow for safe river discharge, was the subject of a research project carried out at the Alexander River basin in Israel. Four pilot-scale units, each about 100 m2, were built: two were designed for subsurface flow with gravel as the medium and two units were designed for free water surface with local soil as the medium. Secondary treated effluent from the Netanya sewage treatment plant was used as the influent. To support the field study and broaden the understanding of the processes involved, two smaller concrete units, 10 m2 each, were built at the Technion site. Results from the first 6 months of the constructed wetlands operation at the Alexander River site and the Technion site showed that the removal of BOD and SS was very efficient under all the conditions studied: retention time of 4–15 days (hydraulic loading of 20–80 m3/0.1 hectare/day) and BOD loading of 1–5.5 kg BOD/0.1 hectare/day. BOD and SS concentrations in treated liquids were always lower than 20 mg/l and most of the time lower than 10 mg/l. However, the removal efficiency of the nitrogen and phosphorous compounds varied within a very wide range; from 95% to as low as zero removal.

Atrazine degradation under denitrifying conditions in continuous culture of Pseudomonas ADP.

The simultaneous removal of atrazine and nitrate in continuous culture under denitrifying conditions using Pseudomonas sp. strain ADP was investigated. Under all operational conditions the nitrate removal efficiency was always higher than 90%, while atrazine degradation deteriorated with time due to contamination by foreign denitrifying bacteria, lacking the ability to degrade atrazine. Recovery of atrazine degradation ability was achieved by applying aerobic conditions with atrazine as the sole nitrogen source.

Xanthan fermentation of citrus waste

Abstract Four different fractions of citrus waste were compared as substrates for xanthan fermentation: whole citrus waste, pectic, hemicellulosic and cellulosic extracts. The whole waste was found to be a good substitute for glucose media for xanthan production. Xanthomonas campestris utilized both simple and complex carbon compounds originating from citrus wastes. Substrate utilization in the medium based on pectin extract was similar to that in the medium based on a whole citrus waste and the pectic extract yielded the same amount of xanthan as the whole waste. This indicated that watersoluble substances in citrus waste such as pectins, organic acids and simple carbohydrates were readily converted into xanthan and that they were the main contributor to xanthan production from the whole waste. The biodegradabilities of the hemicellulose and cellulose extracts were found to be much lower than that of the pectic extract.

Characterization of atrazine degradation and nitrate reduction by Pseudomonas sp. strain ADP

Concomitant atrazine degradation and nitrate reduction by a pure culture of Pseudomonas sp. strain ADP were studied. Under anoxic conditions, Ps ADP grew well and degraded atrazine efficiently in the presence of nitrate. Similar atrazine degradation rates were observed under both anoxic and aerobic conditions: 30.7±2.83 and 36.2±0.44 mg atrazine g−1 cell h−1, respectively. A high denitrification rate of 90.8±8.22 mg NO3−-N g−1 cell h−1 was also observed using Ps ADP with citrate as the electron donor. The required citrate to nitrate ratio for complete denitrification was 5.11±0.15 g citrate g−1 NO3−-N.

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.