David Jeison

Nitrification with high nitrite accumulation for the treatment of wastewater with high ammonia concentration

The objective of this paper was to determine the best conditions for partial nitrification with nitrite accumulation of simulated industrial wastewater with high ammonia concentration, lowering the total oxygen needed in the nitrification step, which may mean great saving in aeration. Dissolved oxygen (DO) concentration and pH were selected as operational parameters to study the possibility of nitrite accumulation not affecting overall ammonia removal. A 2.5L activated sludge reactor was operated in nitrification mode, feeding a synthetic wastewater simulating an industrial wastewater with high ammonia concentration. During the start-up a pH of 7.85 and a DO of 5.5mg/L were used. The reactor was operated until stable operation was achieved at final nitrogen loading rate (NLR) of 3.3kgN- NH(4)(+)/m(3)d with an influent ammonia concentration of 610mg N-NH(4)(+)/L. The influence of pH was studied in continuous operation in the range of 6.15-9.05, changing the reactor pH in steps until ammonia accumulation (complete nitrification inhibition) took place. The influence of DO was studied in the same mode, changing the DO in steps from 5.5 to 0.5mg/L. The pH was not a useful operational parameter in order to accumulate nitrite, because in the range of pH 6.45-8.95 complete nitrification to nitrate occurs. At pH lower than 6.45 and higher than 8.95 complete inhibition of nitrification takes place. Setting DO concentration in the reactor at 0.7mg/L, it was possible to accumulate more than 65% of the loaded ammonia nitrogen as nitrite with a 98% ammonia conversion. Below 0.5mg/L of DO ammonia was accumulated and over a DO of 1.7mg/L complete nitrification to nitrate was achieved. In conclusion, it is possible under the conditions of this study, to treat high ammonia synthetic wastewater achieving an accumulation of at least 65% of the loaded nitrogen as nitrite, operating at a DO around 0.7mg/L. This represents a reduction close to 20% in the oxygen necessary, and therefore a considerable saving in aeration.

Potentials of anaerobic membrane bioreactors to overcome treatment limitations induced by industrial wastewaters

This review presents a comprehensive summary on applications of anaerobic membrane bioreactor (AnMBR) technology for industrial wastewaters in view of different aspects including treatability and filterability. AnMBRs present an attractive option for the treatment of industrial wastewaters at extreme conditions, such as high salinity, high temperature, high suspended solids concentrations, and toxicity that hamper granulation and retention of biomass or reduce the biological activity. So far, most of the research has been conducted at laboratory scale; however, also a number of full-scale AnMBR systems is currently being operated worldwide. Membrane fouling, a multivariable process, is still a research quest that requires further investigation. In fact, membrane fouling and flux decline present the most important reasons that hamper the wide-spread application of full-scale reactors. This paper addresses a detailed assessment and discussion on treatability and filterability of industrial wastewaters in both lab- and full-scale AnMBR applications, the encountered problems and future opportunities.

Anaerobic membrane bioreactors: Are membranes really necessary?

Membranes themselves represent a significant cost for the full scale application of anaerobic membrane bioreactors (AnMBR). The possibility of operating an AnMBR with a self-forming dynamic membrane generated by the substances present in the reactor liquor would translate into an important saving. A self-forming dynamic membrane only requires a support material over which a cake layer is formed, which determines the rejection properties of the system. The present research studies the application of self-forming dynamic membranes in AnMBRs. An AnMBR was operated under thermophilic and mesophilic conditions, using woven and non woven materials as support for the dynamic membranes. Results showed that the formation of a cake layer over the support materials enables the retention of more than 99% of the solids present in the reactor. However, only low levels of flux were achieved, up to 3 L/m2 x h, and reactor operation was unstable, with sudden increases in filtration resistance, due to excessive cake layer formation. Further fine-tuning of the proposed technology involves looking for conditions that can control effectively cake layer formation

Use of Cellulolytic Marine Bacteria for Enzymatic Pretreatment in Microalgal Biogas Production

ABSTRACT In this study, we designed and evaluated a microalgal pretreatment method using cellulolytic bacteria that naturally degrades microalgae in their native habitat. Bacterial strains were isolated from each of two mollusk species in a medium containing 1% carboxymethyl cellulose agar. We selected nine bacterial strains that had endoglucanase activity: five strains from Mytilus chilensis, a Chilean mussel, and four strains from Mesodesma donacium, a clam found in the Southern Pacific. These strains were identified phylogenetically as belonging to the genera Aeromonas, Pseudomonas, Chryseobacterium, and Raoultella. The cellulase-producing capacities of these strains were characterized, and the degradation of cell walls in Botryococcus braunii and Nannochloropsis gaditana was tested with “whole-cell” cellulolytic experiments. Aeromonas bivalvium MA2, Raoultella ornithinolytica MA5, and Aeromonas salmonicida MC25 degraded B. braunii, and R. ornithinolytica MC3 and MA5 degraded N. gaditana. In addition, N. gaditana was pretreated with R. ornithinolytica strains MC3 and MA5 and was then subjected to an anaerobic digestion process, which increased the yield of methane by 140.32% and 158.68%, respectively, over that from nonpretreated microalgae. Therefore, a “whole-cell” cellulolytic pretreatment can increase the performance and efficiency of biogas production.

Microaeration for hydrogen sulfide removal during anaerobic treatment: a review

High sulfide concentrations in biogas are a major problem associated with the anaerobic treatment of sulfate-rich substrates. It causes the corrosion of concrete and steel, compromises the functions of cogeneration units, produces the emissions of unpleasant odors, and is toxic to humans. Microaeration, i.e. the dosing of small amounts of air (oxygen) into an anaerobic digester, is a highly efficient, simple and economically feasible technique for hydrogen sulfide removal from biogas. Due to microaeration, sulfide is oxidized to elemental sulfur by the action of sulfide oxidizing bacteria. This process takes place directly in the digester. This paper reviews the most important aspects and recent developments of microaeration technology. It describes the basic principles (microbiology, chemistry) of microaeration and the key technological factors influencing microaeration. Other aspects such as process economy, mathematical modelling and control strategies are discussed as well. Besides its advantages, the limitations of microaeration such as partial oxidation of soluble substrate, clogging the walls and pipes with elemental sulfur or toxicity to methanogens are pointed out as well. An integrated mathematical model describing microaeration has not been developed so far and remains an important research gap.

Novel technique for measuring the size distribution of granules from anaerobic reactors for wastewater treatment

A new technique for measuring the size distribution of anaerobic granular sludge, which involves the use of digital image analysis, is presented. Sludge samples are embedded in gelatin, spread over glass dishes, which are then placed over a flat-bed scanner where an image is captured. The images are processed with an image analysis software. The technique is simple, reliable and does not need any special equipment.

Effects of the acidogenic biomass on the performance of an anaerobic membrane bioreactor for wastewater treatment.

Continuous flow experiments were performed to study the effects of acidogenic biomass development, induced by feeding with non-acidified substrate, on the operation and performance of an anaerobic membrane bioreactor (AnMBR). The AnMBR was operated at cross-flow velocities up to 1.5m/s and fed with a gelatine-starch-ethanol mixture. A significant fraction of acidogenic biomass developed during reactor operation, which fully determined the sludge rheology, and influenced the particle size distribution. As a result, flux levels of only 6.5l/m(2)h were achieved, at a liquid superficial velocity of 1.5m/s. Even though the soluble microbial products levels in the AMBR were as high as 14g COD/l, the observed hydraulic flux was not limited by irreversible pore fouling, but by reversible cake layer formation. Propionate oxidation was the limiting step for the applied organic loading rate. The assessed specific methanogenic activity (SMA) with propionate as substrate was, however, similar to the values found by others during thermophilic treatment of non or partially acidified substrates in granular sludge bed reactors, indicating an appropriate level of the propionate oxidation capacity.

Impact of high saline wastewaters on anaerobic granular sludge functionalities

Three UASB reactors were operated at different salinity levels in order to assess the effects on the granular sludge properties. High levels of activity inhibition were observed at sodium concentrations over 7 g Na(+)/L, which resulted in low applicable organic loading rates and VFA accumulation in reactor effluents. However, either sludge adaptation or selection for saline resistant microorganisms occurred, which could be concluded from the observed increase in the 50% activity inhibitory concentrations of sodium during continuous flow experiments. Changes in Na(+) susceptibility in time are likely to be expected when treating saline wastewaters. The latter was evidenced by the high sodium tolerance of granular methanogenic sludge coming from a full-scale industrial reactor treating such wastewater. High salinity conditions resulted in a reduced granule strength, predicting process instabilities during long term reactor operation. Batch tests showed that high sodium concentrations seemed to displace the calcium from the granular sludge, a factor known to affect anaerobic granules formation.

Effects of high salinity wastewater on methanogenic sludge bed systems.

The attainable loading potentials of anaerobic sludge bed systems are strongly dependent on the growth of granular biomass with a particular wastewater. Experiments were conducted to determine the effects of high salinity wastewater on the biological and physical properties of methanogenic sludge. Sodium concentration of 5 g/L and 15 g/L were added to the influent of upflow anaerobic sludge bed (UASB) systems. After 100 days of operation, the methanogenic activity, extracellular polymeric substances (EPS), and granular strength were analyzed. The results show a high removal of organic matter but with accumulating propionate concentrations in the effluents. Meanwhile, wash-out of active methanogenic biomass in the effluent of the reactors was observed, likely as a results of the high Na+ concentrations. The rinsed biomass was characterized by a considerable specific methanogenic activity (SMA) on acetate, propionate and hydrogen as the substrates. On the other hand, results show that the SMA evolution was not affected by high salt concentrations. Also the amount and composition of extracellular polymeric substances (EPS) were similar in all sludges. However, results clearly show a sharp drop in the granule strength as a results of high Na+ concentration.

Anaerobic wastewater treatment and membrane filtration: a one night stand or a sustainable relationship?

Several anaerobic membrane bioreactors (AnMBR) were operated, under various conditions, applying different reactor configurations. Applicable fluxes were strongly determined by the physical properties of the sludge present in the reactors. Results show that particle size is a key determining factor for the attainable fluxes. Under thermophilic conditions, small sludge particle size was observed, resulting in low critical fluxes reaching 6-7 L/m2h for the submerged configuration and acidified substrate. In contrast, under mesophilic conditions critical fluxes of 20 L/m2h were obtained. The acidification level also showed a strong effect. Under thermophilic conditions, the presence of a significant fraction of non-acidified organic matter induced the growth of suspended acidogenic biomass that seriously affected the applicable fluxes, both in submerged and side-stream configurations. Under all conditions tested cake formation showed to be the limiting factor determining the applicable fluxes. Only low levels of irreversible fouling were observed. Due to technical and economical considerations, most interesting perspectives for the application of AnMBR are expected with the treatment of high-strength particulate wastewaters, and with extreme wastewaters characterised by high temperature, salinity, etc.