Abstract This manuscript addresses the use of dairy manure wastewater (DMW) as a substrate for methane production in a high rate system - two serial UASB reactors - and the characterization of the effluent in the different phases of the treatment. Two experimental conditions were applied. In the first, the organic load rate (OLR) was 6.2 gCODtotal L-1 d-1 and the hydraulic retention time (HRT) was 12 days, whereas in experiment 2 they were 14.2 gCODtotal L-1 d-1 and 7.5 days, respectively. The reactors showed a high capacity of removal of COD and solids, i.e., above 71%, which led to bioenergy productivities of 0.55 and 0.73 L CH4 L-1 d-1 in experiments 1 and 2,respectively. The methane yield in UASB1 was 0.19 and 0.08 L CH4g CODrem.-1, respectively, inexperiments 1 and 2. The methane yield in UASB1 was greater than UASB2, with approximately 70% of methane content in the biogas in this reactor.The effluent characterization showed micro and macronutrients - some in high concentrations, as nitrogen, phosphorous, K, and Fe between 12.1 and 521.4 mg L-1, and others in low concentrations, as Ca, Mg, Zn and Mn between 0.6 and 13 mg L-1. Na was not removed from the UASB systems and its concentration in the effluent was raised to 23.5% in comparison with the substrate.

A estequiometria de poliânions formados pela ação do ácido nítrico sobre a solução de tungstato de sódio (< 0,01M) foi estudada por meio de técnicas eletrométricas envolvendo titulações potenciométricas e condutométricas. As inflexões e degraus bem definidas nas curvas de titulações forneceram evidências convincentes pela existência de poliânions, para-W12O41(10-) e meta-W12O39(6-) nas faixas do pH 5,7-6,0 e 3,6-4,1; correspondendo a razão H+:WO4(2-) como 7:6 e 9:6, respectivamente. A interação entre soluções de nitrato de lantânio e tungstato de sódio a específicos níveis de pH 8,0; 5,9 e 4,0 também foi estudada por titulações potenciométricas e condutométricas, nos meios aquoso e etanólico, com cada reagente usado alternadamente como titulante. Os experimentos eletrométricos forneceram evidências incontestáveis sobre a formação de tungstatos normal-La2O3.3WO3, para-5La2O3.36WO3 e meta-La2O3.12WO3 nas proximidades de valores de pH 6,3; 5,0 e 4,2; respectivamente. Investigações analíticas sobre os precipitados formados confirmam os resultados do estudo eletrométrico.

The stoichiometry of the polyanions formed by the action of nitric acid on sodium tungstate (< 0.01M) has been studied by means of electrometric techniques involving pH-potentiometric and conductometric titrations. The well defined inflections and breaks in the titration curves provide evidence for the existence of the polyanions, para-W12O41(10-) and meta-W12O39(6-) corresponding to the ratio of H+:WO4(2-) as 7:6 and 9:6 in the pH ranges 5.7-6.0 and 3.6-4.1, respectively. The interaction of lanthanum nitrate with sodium tungstate solutions, at specific pH levels 8.0, 5.9 and 4.0 was also studied by pH and conductometric titrations, in aqueous and alcoholic media, with each of the reagents alternatively used as titrant. The electrometric experiments provide definite evidence of the formation of normal-La2O3.3WO3, para-5La2O3.36WO3 and meta-La2O3.12WO3 tungstates in the vicinity of pH 6.3, 5.0 and 4.2, respectively. Analytical investigations on the precipitates formed confirm the results of the electrometric study.

A natureza precisa da reação entre soluções de ácido nítrico e de ortho-vanadato de sódio foi estudada por técnicas electrométricas envolvendo titulações potenciométricas e condutométricas. As inflexões e degraus bem definidas nas curvas de titulações confirmaram a existencia de anions, piro-V2O7(4-), meta-VO3- e poli-H2V10O28(4-) correspondendo as razões de VO4(3-):H+ como 1:1, 1:2 e 1:2,6 na vizinhança do pH 10,5; 7,4 e 3,6, respectivamente. Ainteração entre soluções de nitrato de cério(III) e vanadato de sódio a específicos níveis de pH 12,4; 10,5; 7,4 e 3,6 também foi estudada por titulações potenciométricas e condutométricas entre os reagentes. Os pontos finais obtidos a partir de inflexções nítidas nas curvas de titulações forceram evidências incontestáveis sobre a formação e precipitação de vanadatos orto-Ce2O3.V2O5, piro-2Ce2O3.3V2 O5 e meta-Ce2O3.3V2O5 de cério nas proximidades dos valores de pH 7,4; 6,2 e 4,8, respectivamente. Investigações analíticas sobre os precipitados formados confirmam os resultados do estudo eletrométrico.

The precise nature of the reaction between nitric acid and sodium ortho-vanadate solutions has been studied by means of electrometric techniques involving potentiometric and conductometric titrations. The well defined inflections and breaks in the titration curves confirm the existence of the anions, pyro-V2O7(4-), meta-VO3- and poly-H2V10O28(4-) corresponding to the ratios of VO4(3-):H+ as 1:1, 1:2 and 1:2.6 in the neighborhood of pH 10.5, 7.4 and 3.6, respectively. The interaction of cerium(III) nitrate with sodium vanadate solutions, at specific pH levels 12.4, 10.5, 7.4 and 3.6 was also studied by potentiometric and conductometric titrations between the reactants. The end-points obtained from the sharp inflections in the titration curves provide definite evidence for the formation and precipitation of cerium ortho-Ce2O3.V2O5, pyro-2Ce2O3.3V2O5 and meta-Ce2O3.3V2O5 vanadates in the neighborhood of pH 7.4, 6.2 and 4.8, respectively. Analytical investigations on the precipitates formed confirm the results of the electrometric study.