Pedro A. García-Encina

Influence of pH over nitrifying biofilm activity in submerged biofilters

Abstract The influence of pH over nitrification in submerged biofilters has been studied through the observation of three pH effects over the nitrifying biofilm: activation-deactivation, substrate limitation, and free ammonia inhibition. Within a pH range of 5.0–9.0, a pH increase of one unit produce a 13% increase on the nitrification efficiency. A stoichiometry of 7.1 mg CaCO 3 /mg N was measured for the process, which became alkalinity limited below pH 5.0. The highest activity of ammonium oxidizers and the highest values of volatile attached solids (VAS) in the filter were obtained at pH 8.2. The concentration of volatile attached solids (VAS) was regulated by free ammonia inhibition, substrate limitation (NH 4 + concentration), and reactor hydrodynamics. Inhibition by free ammonia controlled bacteria activity at pH greater than 7.5, observing an increase of microorganisms concentration in the filter as a specific free ammonia concentration (mg NH 3free -N gVAS −1 ) decreased. A nitrite accumulation of up to 80–90% was obtained for specific inhibitory concentrations greater than 1.5 mg NH 3free -N gVAS −1 resulting from the selective inhibition of nitrite oxidizers.

Long-term operation of high rate algal ponds for the bioremediation of piggery wastewaters at high loading rates.

The performance of two 464-L high rate algal ponds (HRAPs) treating 20- and 10-folds diluted swine manure at 10 days of hydraulic residence time was evaluated under continental climatic conditions in Castilla y Leon (Spain) from January to October. Under optimum environmental conditions (from July to September), both HRAPs supported a stable and efficient carbon and nitrogen oxidation performance, with average COD and TKN removal efficiencies of 76+/-11% and 88+/-6%, respectively, and biomass productivities ranging from 21 to 28 g/m(2)d. Nitrification was identified as the main TKN removal mechanism at dissolved oxygen concentrations higher than 2mg/L (accounting for 80-86% of the TKN removed from January to May and for 54% from July to September). On the other hand, empirical evidences of a simultaneous nitrification-denitrification process were found at dissolved oxygen concentrations lower than 0.5mg/L (high organic loading rates). However, despite the achievement of excellent COD and nitrogen oxidation performance, phosphorous removal efficiencies lower than 10% were recorded in both HRAPs probably due to the high buffer capacity of the piggery wastewater treated (absence of abiotic pH-mediated PO(4)(3-) precipitation). Finally, a detailed monitorization of the dynamics of microalgae population revealed that the combination of moderate temperatures/solar irradiances and high organic loading rates, prevailing during late spring and summer, supported higher microalgae diversities than those found during winter conditions.

The use of methane as a sole carbon source for wastewater denitrification

Abstract This paper presents the results obtained in wastewater denitrification studies using methane as sole carbon source under two different conditions—i.e. in the presence of oxygen and under strict anoxic conditions. In the latter case, no significant denitrification was observed. However, in the presence of oxygen, a successful denitrification was obtained in batch reactors with a denitrification rate reaching 0.6 kg N-NO3− kg−1 VSS per day. It was shown that nitrate consumption could not be solely attributed to nitrogen assimilation and from 5 to 75% of the initial N-NO3− was escaping from the reactors in gaseous form. An important wasteful methane oxidation (indirectly related to denitrification) was also observed reaching in some experiment 90% of the total methane oxidation. The system obtained appeared to consist of an association of methanotrophic bacteria, oxidising methane and producing one or several intermediate organic compounds, still unidentified, which are later consumed by the denitrifying bacteria. No evidence was found for the involvement of methanol or acetate as intermediates, as suggested by the literature.

A comparative evaluation of microalgae for the degradation of piggery wastewater under photosynthetic oxygenation

Two green microalgae (Scenedesmus obliquus and Chlorella sorokiniana), one cyanobacterium (Spirulina platensis), one euglenophyt (Euglena viridis) and two microalgae consortia were evaluated for their ability to support carbon, nitrogen and phosphorous removal in symbiosis with activated sludge bacteria during the biodegradation of four and eight times diluted piggery wastewater in batch tests. C. sorokiniana and E. viridis were capable of supporting the biodegradation of four and eight times diluted wastewater. On the other hand, while S. obliquus and the consortia isolated from a swine manure stabilization pond were only able to grow in eight times diluted wastewater, S. platensis and the consortium isolated from a high rate algal pond treating swine manure were totally inhibited regardless of the dilution applied. TOC removal efficiencies (RE) ranging from 42% to 55% and NH(4)(+)-RE from 21% to 39% were recorded in the tests exhibiting photosynthetic oxygenation. The similar oxygen production rates exhibited by the tested microalgae under autotrophic conditions (from 116 to 133mgO(2)L(-1)d(-1)) suggested that factors other than the photosynthetic oxygenation potential governed piggery wastewater biodegradation. Microalgal tolerance towards NH(3) was hypothesized as the key selection criterion. Further studies in a continuous algal-bacterial photobioreactor inoculated with C. sorokiniana, S. obliquus and S. platensis showed that C. sorokiniana, the species showing the highest NH(3)-tolerance, rapidly outcompeted the rest of the microalgae during the biodegradation of eight times diluted wastewater, achieving TOC and NH(4)(+)-RE comparable to those recorded in the batch biodegradation tests.

Coagulation/flocculation-based removal of algal–bacterial biomass from piggery wastewater treatment

Two conventional chemical coagulants (FeCl3 and Fe2(SO4)3) and five commercial polymeric flocculants (Drewfloc 447, Flocudex CS/5000, Flocusol CM/78, Chemifloc CV/300 and Chitosan) were comparatively evaluated for their ability to remove algal-bacterial biomass from the effluent of a photosynthetically oxygenated piggery wastewater biodegradation process. Chlorella sorokiniana, Scenedesmus obliquus, Chlorococcum sp. and a wild type Chlorella, in symbiosis with a bacterial consortium, were used as model algal-bacterial consortia. While the highest biomass removals (66-98%) for the ferric salts were achieved at concentrations of 150-250 mg L(-1), dosages of 25-50 mg L(-1) were required for the polymer flocculants to support comparable removal efficiencies. Process efficiency declined when the polymer flocculant was overdosed. Biomass concentration did not show a significant impact on flocculation within the concentration range tested. The high flocculant requirements herein recorded might be due to the competition of colloidal organic for the flocculants and the stationary phase conditions of biomass.

Odor abatement in biotrickling filters: Effect of the EBRT on methyl mercaptan and hydrophobic VOCs removal

The performance and microbiology of a biotrickling filter (BTF) treating methyl mercaptan, toluene, alpha-pinene and hexane at the mg m(-3) level was studied at empty bed residence times (EBRT) of 50, 30, 11 and 7 s. Removal efficiencies (REs) higher than 95% were observed for MeSH, toluene and alpha-pinene even at 11 s, while hexane REs exceeded 70%. At 7 s, an irreversible damage of the microbial activity due to the accumulation of toxic metabolites resulted in a decrease of REs. The addition of silicone stabilized process performance but only re-inoculation allowed achieving a complete removal of MeSH, toluene and alpha-pinene, and hexane REs of 80%. The high K(L)a values (ranging from 38 ± 4 to 90 ± 11 h(-1)) explained the good BTF performance at such low EBRTs. A high bacterial diversity, along with a vertical distribution of the bacterial communities was observed, the main phyla being Proteobacteria, Actinobacteria, Nitrospira, Chloroflexi and Gemmatimonadertes.

Denitrification with methane as electron donor in oxygen-limited bioreactors

Abstract The microbial population from a reactor using methane as electron donor for denitrification under microaerophilic conditions was analyzed. High numbers of aerobic methanotrophic bacteria (3 107 cells/ml) and high numbers of acetate-utilizing denitrifying bacteria (2 107 cells/ml) were detected, but only very low numbers of methanol-degrading denitrifying bacteria (4 104 cells/ml) were counted. Two abundant acetate-degrading denitrifiers were isolated which, based on 16S rRNA analysis, were closely related to Mesorhizobium plurifarium (98.4% sequence similarity) and a Stenotrophomonas sp. (99.1% sequence similarity). A methanol-degrading denitrifying bacterium isolated from the bioreactor morphologically resembled Hyphomicrobium sp. and was moderately related to H. vulgare (93.5% sequence similarity). The initial characterization of the most abundant methanotrophic bacterium indicated that it belongs to class II of the methanotrophs. “In vivo”13C-NMR with concentrated cell suspensions showed that this methanotroph produced acetate under oxygen limitation. The microbial composition of reactor material together with the NMR experiments suggest that in the reactor methanotrophs excrete acetate, which serves as the direct electron donor for denitrification.

Influence of flue gas sparging on the performance of high rate algae ponds treating agro-industrial wastewaters.

The influence of flue gas sparging (7% CO(2)) on the performance of two 465 L High-Rate Algal Ponds (HRAPs) treating diluted swine manure at 10 days of hydraulic retention time was evaluated under continental climatic conditions (Castilla y León, Spain). COD, NH(4)(+), and PO(4)(3-) removal efficiencies were not significantly affected by flue gas input (at 2.2 and 5.5 L min(-1)), which suggests that CO(2) sparging does not compromise wastewater treatment in HRAPs. In this particular study, COD and NH(4)(+) removal efficiencies of 56+/-31% (near to maximum swine manure biodegradability) and 98+/-1%, respectively, were consistently maintained, regardless of the environmental and operational conditions. CO(2) sparging resulted however in lower pH values (approximately 2 units lower) and an enhanced NH(4)(+) nitrification (higher NO(3)(-) and NO(2)(-) concentrations) compared to the system operated in the absence of flue gas supply. Biomass concentration was only higher (approximately 30% than in the control HRAP) when flue gases were supplied at 5.5 L min(-1), probably due to the fact that the higher irradiances and temperatures prevailing within this experimental period resulted in an inorganic carbon-limited scenario in the control HRAP. Therefore, it can be concluded that CO(2) assimilation would be ultimately dependent on the occurrence of inorganic carbon limitation and will never occur in light, COD or nutrients-limited scenarios.

Different pretreatments for increasing the anaerobic biodegradability in swine manure

The effect of three methods (mechanical, chemical, and thermal pretreatment) were tested to improve methane production and anaerobic biodegradability of swine wastes. The first experiment was designed to determine the biodegradability enhancement through the separation of liquid and solid matrix by using a 0.25mm pore size screen (mechanical pretreatment). The second approach was the treatment of swine waste by the addition of a flocculant agent and strong chemicals such as acid (HCl) and alkali (NaOH). The third pretreatment studied was thermal application (170 degrees C provided by vapor). The soluble COD was increased by 57% and 32% during the pretreatment period with alkali and thermal application, respectively. In addition, these two pretreatments gave the highest enhancement on methane production with regard to the untreated sample. Meanwhile, the addition of a flocculant improved the methane production of the liquid fraction but not the solid one. On the other hand, mechanical pretreatment did not show any important enhancement. Biodegradability percentage followed the same trend as methane productivity.

Influence of Biogas Flow Rate on Biomass Composition During the Optimization of Biogas Upgrading in Microalgal-Bacterial Processes

The influence of biogas flow rate (0, 0.3, 0.6, and 1.2 m(3) m(-2) h(-1)) on the elemental and macromolecular composition of the algal-bacterial biomass produced from biogas upgrading in a 180 L photobioreactor interconnected to a 2.5 L external bubbled absorption column was investigated using diluted anaerobically digested vinasse as cultivation medium. The influence of the external liquid recirculation/biogas ratio (0.5 < L/G < 67) on the removal of CO2 and H2S, and on the concentrations of O2 and N2 in the upgraded biogas, was also evaluated. A L/G ratio of 10 was considered optimum to support CO2 and H2S removals of 80% and 100%, respectively, at all biogas flow rates tested. Biomass productivity increased at increasing biogas flow rate, with a maximum of 12 ± 1 g m(-2) d(-1) at 1.2 m(3) m(-2) h(-1), while the C, N, and P biomass content remained constant at 49 ± 2%, 9 ± 0%, and 1 ± 0%, respectively, over the 175 days of experimentation. The high carbohydrate contents (60-76%), inversely correlated to biogas flow rates, would allow the production of ≈100 L of ethanol per 1000 m(3) of biogas upgraded under a biorefinery process approach.