Experimental study of abattoir wastewater treatment from an economic perspective

The most cost effective treatment scheme for effluent from Midfield Meats, an abattoir in Warrnambool, Australia, was evaluated via a series of laboratory and commercial scale experiments. Effectiveness was measured in terms of suspended solids (SS) and biological oxygen demand (BOD) reduction. Economic assessment was based on predicted reduction in trade waste charges versus infrastructure and running costs. From the range of potential treatment technologies, those deemed most appropriate for trialling included pre-screening, sedimentation, coagulation and flocculation treatment and dissolved air floatation (DAF). Prior to evaluation of treatment types, flow, loads and contaminant characterisation of the waste streams was conducted to aid in selection of treatment type and capacity. Prescreening was found to be the most cost effective, followed by sedimentation, coagulation and flocculation treatment and finally DAF. The most economical treatment scheme that satisfied the requirements of Midfield Meats included a combination of prescreening and sedimentation. DAF and coagulation and flocculation treatment satisfactorily treated the wastewater, however were not cost effective under the current trade waste agreement.

Direct measurement of surface forces due to charging of solids immersed in a nonpolar liquid

Direct measurements of a long-range force between charged solid surfaces in a nonpolar liquid are presented for the first time. Measurements were made between mica surfaces in solutions of the anionic surfactant sodium di-2-ethylhexylsulfosuccinate (AOT) at millimolar concentrations in n-decane using a surface force apparatus which has been modified to improve its sensitivity for detecting a weak and long-range force. Modifications include a magnetic drive system, the use of a weak cantilever spring with the apparatus mounted in a vertical configuration, and a detailed consideration of the interference optics to allow accurate measurements of surface separations up to several micrometers. The results show a repulsion that is well fitted by theoretical curves based on a model in which only counterions enter the calculation, in other words, in the absence of a reservoir of ions in the solvent. Fitting the theory to the data allows an estimate of the mica surface charge density of ∼1 mC/m². A mechanism for surface charging of mica in this solution is proposed, which includes a role for trace amounts of water that are inevitably present and adsorbed surface aggregates of AOT. The relevance of the results to previously observed charge stabilization of colloids in nonaqueous solvents is discussed.

Measurement of the deformation and adhesion of solids in contact

Two curved surfaces of molecularly smooth mica are brought into contact under a controlled load, and their deformed shape is measured using optical interference fringes of equal chromatic order. This technique allows exceptionally accurate measurements of surface profiles at separations down to a molecular scale. Contact between the surfaces can be made either adhesive or nonadhesive by suitable choice of the medium between them. Results have been obtained in both cases and compared with the theories of Hertz (nonadhesive contact) and Johnson, Kendall, and Roberts (adhesive contact).

Comparison of various NMR methods for the indirect detection of nitrogen-14 nuclei via protons in solids

We present an experimental comparison of several through-space Hetero-nuclear Multiple-Quantum Correlation experiments, which allow the indirect observation of homo-nuclear single- (SQ) or double-quantum (DQ) ¹⁴N coherences via spy ¹H nuclei. These ¹H-{¹⁴N} D-HMQC sequences differ not only by the order of ¹⁴N coherences evolving during the indirect evolution, t1, but also by the radio-frequency (rf) scheme used to excite and reconvert these coherences under Magic-Angle Spinning (MAS). Here, the SQ coherences are created by the application of center-band frequency-selective pulses, i.e. long and low-power rectangular pulses at the ¹⁴N Larmor frequency, ν0(¹⁴N), whereas the DQ coherences are excited and reconverted using rf irradiation either at ν0(¹⁴N) or at the ¹⁴N overtone frequency, 2ν0(¹⁴N). The overtone excitation is achieved either by constant frequency rectangular pulses or by frequency-swept pulses, specifically Wide-band, Uniform-Rate, and Smooth-Truncation (WURST) pulse shapes. The present article compares the performances of four different ¹H-{¹⁴N} D-HMQC sequences, including those with ¹⁴N rectangular pulses at ν0(¹⁴N) for the indirect detection of homo-nuclear (i) ¹⁴N SQ or (ii) DQ coherences, as well as their overtone variants using (iii) rectangular or (iv) WURST pulses. The compared properties include: (i) the sensitivity, (ii) the spectral resolution in the ¹⁴N dimension, (iii) the rf requirements (power and pulse length), as well as the robustness to (iv) rf offset and (v) MAS frequency instabilities. Such experimental comparisons are carried out for γ-glycine and l-histidine.HCl monohydrate, which contain ¹⁴N sites subject to moderate quadrupole interactions. We demonstrate that the optimum choice of the ¹H-{¹⁴N} D-HMQC method depends on the experimental goal. When the sensitivity and/or the robustness to offset are the major concerns, the D-HMQC sequence allowing the indirect detection of ¹⁴N SQ coherences should be employed. Conversely, when the highest resolution and/or adjusted indirect spectral width are needed, overtone experiments are the method of choice. The overtone scheme using WURST pulses results in broader excitation bandwidths than that using rectangular pulses, at the expense of reduced sensitivity. Numerically exact simulations also show that the sensitivity of the overtone ¹H-{¹⁴N} D-HMQC experiment increases for larger quadrupole interactions.

Avaliação do processo de compostagem de resíduos sólidos urbanos

A crescente produção de resíduos sólidos urbanos e a escassez de áreas para uma destinação final tecnicamente adequada, via implantação de aterros sanitários, faz com que tome importância a técnica de tratamento de resíduos sólidos orgânicos através das compostagem/vermicompostagem. Nesta pesquisa, foi realizada a avaliação destes processos, tendo sido observadas principalmente a influência da aeração e da umidade no desempenho destas técnicas de tratamento, em leiras de pequenos e grandes volumes. Nos experimentos, com leiras de pequenos volumes, realizados no IPH (Instituto de Pesquisas Hidráulicas) da UFRGS, utilizou-se resíduos sólidos de poda (resíduos verdes, com alta concentração de carbono) codispostos (misturados em peso) com resíduos vegetais da CEASA (Companhia Estadual de Abastecimento Sociedade Anônima) e lodos provenientes de estações de tratamento de esgotos sanitários. Nos experimentos, com leiras de grandes volumes, realizados na UTC – Unidade de Triagem e Compostagem de Porto Alegre, utilizou-se resíduos orgânicos domiciliares codispostos com os mesmos resíduos utilizados nos primeiros experimentos. Paralelamente aos experimentos de compostagem, avaliou-se os lixiviados produzidos nos sistemas. Na compostagem de grandes volumes, também foi observado o desempenho de banhados construídos de fluxo subsuperficial para o tratamento desses efluentes líquidos. com teores de resíduos verdes menores que 35 %, o que se justifica pela maior concentração de resíduos de característica facilmente biodegradável e de maior palatabilidade para os vermes. Em todos os experimentos de compostagem, verificou-se que o controle efetivo do processo pode ser realizado através da avaliação sistemática das temperatura e umidade das leiras. Evidenciou-se também que para regiões de clima similar ao de Porto Alegre, com elevadas precipitações principalmente no inverno, é necessário adotar dimensões adequadas ao sistema de compostagem “windrow” para áreas descobertas. Comprovou-se também a necessidade de manutenção da umidade na faixa entre 50% e 70 %, inclusive com reposição desta, mesmo na situação de inverno. A avaliação dos lixiviados da compostagem demonstrou que, com os substratos utilizados nos experimentos, as concentrações de DBO5, DQO e de outras variáveis são elevadas ao início do processo de decomposição, devido à solubilização dos compostos orgânicos e inorgânicos presentes na matéria orgânica. Os lixiviados da compostagem possuem baixas concentrações de condutividade, DBO5, NH4 +, entre outros, quando comparados aos lixiviados de aterros sanitários. tratamento destes efluentes. Os resultados obtidos nos banhados construídos para baixas cargas hidráulicas (1cm/d) e concentrações de DBO5 do afluente abaixo de 150 mg/L apontaram uma eficiência média de remoção de 52,02%. No que se refere a nitrogênio (todas as formas), fósforo, metais, potencial redox e sólidos totais, as eficiências foram variáveis, com melhores resultados para nitrogênio amoniacal e fósforo. A compostagem pode ser considerada uma alternativa viável de tratamento de resíduos orgânicos, utilizando-se o processo “windrow” com revolvimento mecânico, mesmo em pátios descobertos em climas subtropicais. Neste caso, sugere-se que os lixiviados gerados nos primeiros dias de compostagem (30 dias aproximandamente) sejam recirculados e o excedente tratado em ETE. Pode-se, também, utilizar o sistema de banhados construídos como complementação, principalmente para a remoção de nitrogênio e fósforo.

Rhamnolipid produced from agroindustrial wastes enhances hydrocarbon biodegradation in contaminated soil

A crude biosurfactant solution was produced by Pseudomonas aeruginosa growing on agroindustrial wastes as the substrate and used to study its effect on hydrocarbon biodegradation by the indigenous soil microflora under laboratory conditions. Two concentrations were studied at first and 1 mg of biosurfactant/g of soil showed to be the most efficient for the total petroleum hydrocarbon reduction, which reached 85% at the first 20 days in soil microcosms. Respirometric and microbial analyses showed that the biosurfactant added did not have toxic effects over the microbial population. The use of a biosurfactant for bioremediation has been limited because of its high cost production. Biosurfactants produced from cost-free by-products combines waste minimization with economic potential bioremediation process.