Anaerobic biodegradability of water separated from extracted crude oil

Abstract

A study of the anaerobic biodegradability of the three categories of water separated from extracted crude oil (Venezuelan oilfields)--light, medium or heavy crude--was carried out at laboratory scale using UASB reactors working at mesophilic conditions. Chemical oxygen demand (COD) removal in a low loaded UASB reactor fed with water separated from extracted light crude was high, with an average 87% purification efficiency. The remaining COD was made up of the nonbiodegradable and the very slowly biodegradable fractions of the organic matter in the water. During a second period, the hydraulic retention time was reduced in stages, thus increasing the loading rate. In the experimental conditions used, COD concentration at the outlet remained below the Venezuelan standard limit for discharge into the environment (350 mg COD l(-1)) when the hydraulic retention time (HRT) was above 10 hours and the OLR under 3 g COD l(-1) d(-1). For HRT less than 10 hours, or organic loading rate (OLR) greater than 3 g COD l(-1) d(-1), COD at the outlet of the reactor rose as a consequence both of increased volatile fatty acids (VFA) concentrations (indicating an overloading of the methanogenic population) and, also, of the increase in the non-VFA COD (indicating a decrease in the acidification efficiency). On the other hand, results with UASB reactors operated at a low loading rate and fed with water separated from extracted medium and heavy crude oil showed that purification efficiency was low, with only 20% and 37% COD removal respectively. Continuing the operation of the UASB reactor fed with water separated from medium oil over a prolonged period did not bring any improvement, indicating that no adaptation of the sludge occurred.

Biological treatment of oil and gas produced water: a review and meta-analysis

“…Different configurations of anaerobic treatment were used. In four studies, upflow anaerobic sludge blanket (UASB) reactors were used, and in two studies fixed-film media were incorporated into the UASB (Ghorbanian et al 2014;Khong et al 2012;Liu et al 2013;Rincon et al 2003). Liu et al (2013) used a UASB followed by an aerated biological filter.…”

“…Control of hydrogen sulfide-done by altering the pH and periodically purging with nitrogen gas-was an issue in another study (Vieira et al 2005). Rincon et al (2003) studied produced waters originating from the separation of light, medium, and heavy crude oil, which yielded different COD removal rates (87, 20 and 37%), demonstrating treatment variability depending on the produced water characteristics.…”

Diversidad microbiológica del lodo anaerobio durante el tratamiento de aguas de producción petroleras venezolanas

“…En la digestión anaeróbica el pH es, en general, amortiguado por el bicarbonato, dependiendo así de la capacidad buffer expresada en alcalinidad total. Por tanto, es posible inferir que la diferencia en el pH de los efluentes tratados sea debida a la composición de las APP, las cuales tienen una gran capacidad amortiguadora resultante de la concentración de iones carbonatos y bicarbonatos (Rincón et al, 2003). La alcalinidad total media en el efluente de los reactores UASB alimentados con glucosa y APP fue de 632.3 ± 68.2 y 1815.5 ± 144.7 mgCaCO 3 /L, respectivamente.…”

“…Las densidades de los diferentes grupos microbianos estudiados durante la etapa de estabilidad en los reactores UASB alimentados con glucosa y APP fueron significativamente diferentes (p < 0.05), exceptuando a las BNR (figura 1). El orden de abundancia de los grupos funcionales fue mayor para la glucosa (10 8 ) que para las APP (10 5 ), lo cual pudiera ser un indicativo de la inhibición del crecimiento debido a la presencia de compuestos tóxicos en las APP, de acuerdo con lo reportado en otros estudios (Chen et al, 2008;Liu et al, 2008;Rincón et al, 2003).…”

“…La digestión anaerobia en reactores de manto de lodo con flujo ascendente (UASB), ha sido evaluada satisfactoriamente a escala de laboratorio, como alternativa real para el tratamiento de estas aguas de producción, mostrando la factibilidad técnica para su biodegradabilidad anaerobia (Díaz et al, 2005;Rincón et al, 2003;Rincón et al, 2002). Una gran variedad de microorganismos coexisten en el lodo de estos reactores anaerobios y la combinación apropiada de los mismos es necesaria para una eficiente transformación de la materia orgánica a gas metano (Hori et al, 2005).…”