F. Esparza-García

Inhibition of mesophilic solid-substrate anaerobic digestion by ammonia nitrogen

Abstract This work focused on determining the effects of ammonia-nitrogen supplementation on the mesophilic solid-substrate anaerobic digestion of municipal wastes and waste activated sludge (biosolids). Bench-scale, semi-continuous, mesophilic reactors were operated with a 21-day mass-retention time and dosed with NH4Cl, such that the corresponding chemical O2 demand (COD)/N ratios in their feeds were 90, 80, 65 and 50 (reactors R1 or control, R2, R3 and R4 respectively). Reactor performance was evaluated in terms of the efficiency of volatile solid removal (efficiency for short), biogas productivity, methane content in the biogas, pH and volatile organic acid contents, among other monitoring and analytical parameters. The feedstock was a mixture of urban wastes with biosolids. It was found that the process performance deteriorated at increasing dosages of ammonia N, the process practically ceasing at COD/N = 50 (R4). Inhibition was characterized by efficiency and biogas productivity decreases and a more sudden drop of methane content in biogas and pH. A significant rise of propionic, butyric and valeric acid was found in reactors receiving the highest doses of ammonia N (R3 and R4). This suggested that inhibition of the syntrophic bacteria present in the anaerobic consortia also occurred. Luong and Pearson inhibition models were fitted to the data. Both models represented very well the acute effects of N supplementation on solid-substrate anaerobic digestion. However, the Luong model could also represent the process ceasing at a critical ammonia N concentration of 2800 mg/kg mixed solids.

Scenedesmus incrassatulus CLHE-Si01: a potential source of renewable lipid for high quality biodiesel production.

The potential of microalgal oil from Scenedesmus incrassatulus as a feedstock for biodiesel production was studied. Cell concentration of S. incrassatulus and lipid content obtained during mixotrophic growth were 1.8 g/L and 19.5 ± 1.5% dry cell weight, respectively. The major components of biodiesel obtained from S. incrassatulus oil were methyl palmitate (26%) and methyl linoleate (49%), which provided a strong indication of high quality biodiesel. Fuel properties were determined by empirical equations and found to be within the limits of biodiesel standard ASTM D6751 and EN 14214. The quality properties of the biodiesel were high cetane number (62), low density (803 kg/m(3)), low viscosity (3.78 mm(2)/s), oxidation stability (9h) and cold filter plugging point (-4°C). Hence, S. incrassatulus has potential as a feedstock for the production of excellent quality biodiesel.

Short-Term Accumulation of Atrazine by Three Plants from a Wetland Model System

This work describes the accumulation and distribution of the herbicide atrazine in soil, water, and roots from three wetland model systems using the monocots Typha domingensis, Sagittaria lancifolia, and Echinochloa pyramidalis. Results were analyzed from a 33 full factorial experimental design, in order to describe the effect of accumulation of atrazine and times of exposure in the species evaluated. We found that accumulation depends on the species and the herbicide concentration; about 30% was accumulated in soil, 40% in roots, and 10–20% in water. By the end of the experiment, E. pyramidalis accumulated 8.47 mg/l of atrazine and 14.39 mg/l T. domingensis; in all cases, adsorption accounted for 1.4%, fitting a Langmuir model with a kd of 14.47.

Fractionation and availability of heavy metals in tannery sludge-amended soil and toxicity assessment on the fully–grown Phaseolus vulgaris cultivars

This study was conducted to assess the effect of tannery sludge on the bush bean (Phaseolus vulgaris) cultivars fully–grown on a culture sandy soil, as tannery sludge is valuable to improve soil fertility but long term studies evaluating the effect on fully grown plants are scarce. Tannery sludge amendments (0, 0.77, 1.54, 3.08 and 6.16 g tannery sludge kg−1 soil) were characterized and the main heavy metals identified (Cr, Mn, Fe, K, and Zn) later on sequentially and singly extracted, for soil fractionation and availability determination, respectively. Metals showed different fractionation and availability patterns, being the most toxic metal (Cr) found to primarily bind to the carbonate fraction in soil, while almost 10% of the total Cr was available for plant uptake. In the green house experiments, bush bean cultivars exposed to increasing tannery sludge amendments were evaluated at different plant stages. Metal accumulation and physiological parameters (chlorophyll, carotenoids, nitrate reductase activity and dry weight) were determined. Toxicity was primarily due to Cr, stimulating or affecting the response of physiological parameters and suppressing seed formation at the highest tannery sludge ratio. Metals were mainly accumulated in the roots of bush beans, diminishing in the upper part of the plants with minimal translocation to seeds, supposing little risk for human consumption. Additionally, important correlations, antagonistic and synergistic relationships were observed between the extracted metals and metal accumulation in plant tissues.

Application of 2III7-3 fractional factorial experimental design to enhance enzymatic activities of Pleurotus ostreatus with high concentrations of polychlorinated biphenyls.

A 2III 7−3 fractional factorial experimental design was used to establish 16 culture media, with and without PCBs to enhance the activities of laccase (Lac), manganese peroxidase (MnP), and versatile peroxidase (VP) produced by the white rot fungus Pleurotus ostreatus. The culture was added to 10,000 mg L−1 of transformer oil, containing 71% of the identified Arochlor 1242. The culture conditions were established with eight variables at two values (levels); pH (4 and 6), agitation (100 and 200 rpm), CuSO4 (150 and 250 mg L−1), MnSO4 (50 and 200 mg L−1), Tween 80 (13 and 3500 mg L−1), wheat straw (0 and 2.5 g L−1), sugarcane bagasse (0 and 2.5 g L−1),and Arochlor 1242 (0 and 7100 mg L−1) at 4, 8, 12, 16 and 20 days old culture. Laccase activity was enhanced at a high value of pH and low value of agitation (P<0.001) and correlated positively (R2= 0.9; α=0.05) with the removal of polychlorinated biphenyls (PCBs). VP activity was enhanced 27-fold with PCBs, Tween 80 and pH. The MnP activity was increased 1.2-fold with PCBs. The fractional factorial experimental design methodology allowed us to determine the P. ostreatus culture media conditions to enhance Lac and VP activities for efficient removal of Arochlor 1242 (one of the most recalcitrant organochloride pollutants). The factors that shown the greatest effect on Lac activity were: pH, agitation and high concentrations of Arochlor 1242.