Sandra Esteves - Academia.edu (original) (raw)

Papers by Sandra Esteves

Bioresource Technology, Nov 1, 2013

The production of polyhydroxyalkanoates (PHAs) using digestate liquor as culture media is a novel... more The production of polyhydroxyalkanoates (PHAs) using digestate liquor as culture media is a novel application to extend the existing uses of digestates. In this study, two micro-filtered digestates (0.22 μm) were evaluated as a source of complex culture media for the production of PHA by Cupriavidus necator as compared to a conventional media. Culture media using a mixture of micro-filtered liquors from food waste and from wheat feed digesters showed a maximum PHA accumulation of 12.29 g/l PHA, with 90% cell dry weight and a yield of 0.48 g PHA/g VFA consumed, the highest reported to date for C. necator studies. From the analysis of the starting and residual media, it was concluded that ammonia, potassium, magnesium, sulfate and phosphate provided in the digestate liquors were vital for the initial growth of C. necator whereas copper, iron and nickel may have played a significant role in PHA accumulation.

Bioresource Technology, Jul 1, 2014

h i g h l i g h t s NaCl is a low cost and sustainable external stress that can enhance PHA produ... more h i g h l i g h t s NaCl is a low cost and sustainable external stress that can enhance PHA production. NaCl addition at 9 g/l resulted in 30% more and an earlier PHA accumulation. Addition of 12 and 15 g/l NaCl were found to inhibit the production of PHA. A dielectric spectroscopy probe was able to indicate PHA accumulation in real-time. The window for maximum accumulation was detected by the probe avoiding polymer loss.

Bioresource Technology, Aug 1, 2011

A life cycle assessment has been completed of potential biogas infrastructures on a regional scal... more A life cycle assessment has been completed of potential biogas infrastructures on a regional scale. Centralised and distributed infrastructures were considered along with biogas end uses of Combined Heat and Power (CHP) and injection to the gas grid for either transport fuel or domestic heating end uses. Damage orientated (endpoint) life cycle impact assessment method identified that CHP with 80% heat utilisation had the least environmental impact, followed by transport fuel use. Utilisation for domestic heating purposes via the gas grid was found to perform less well. A 32% difference in transportation requirement between the centralised and distributed infrastructures was found to have a relatively small effect on the overall environmental impact. Global warming impacts were significantly affected by changes in methane emissions at upgrading stage, highlighting the importance of minimising operational losses.

Bioresource Technology, Dec 1, 2017

The integration of a biomethanation system within a wastewater treatment plant for conversion of ... more The integration of a biomethanation system within a wastewater treatment plant for conversion of CO2 and H2 to CH4 has been studied. Results indicate that the CO2 could be utilised to produce an additional 13,420 m 3 / day of CH4, equivalent to approximately 133,826 kWh of energy. The whole conversion process including electrolysis was found to have an energetic efficiency of 66.2 %. The currently unoptimised biomethanation element of the process had a parasitic load of 19.9 % of produced energy and strategies to reduce this to <5 % are identified. The system could provide strategic benefits such as integrated management of electricity and gas networks, energy storage and maximising the deployment and efficiency of renewable energy assets. However, no policy or financial frameworks exist to attribute value to these increasingly important functions.

Bioresource Technology, Jun 1, 2018

Biotechnology and Bioprocess Engineering, Nov 1, 2014

In this study volatile fatty acids (VFAs), which are by-products from anaerobic fermentations, ha... more In this study volatile fatty acids (VFAs), which are by-products from anaerobic fermentations, have been used as the carbon source for polyhydroxyalkanoates (PHA) production by pure culture bacteria, Cupriavidus necator. A number of factors influence the conversion efficiencies of VFAs to PHAs including the bacterial feeding regimes. When VFA was supplied as a single feed, it was found that concentrations higher than 2% v/v VFA led to substrate inhibition and only 18% acetic acid and 12% of butyric acid was converted into PHA. This resulted in less than 65% (w/w) of PHA content within the microbial cells. Hence, the single VFA feeding strategy was found to provide low conversion rates of VFA into polymer. An improved feeding strategy was found to be the use of an automatic VFA feed based on the pH control of the medium, which led to a more continuous feeding regime. The conversion of VFA to PHA was increased by almost 2-fold to 33 and 22% for acetic acid and butyric acid respectively, with up to 75% (w/w) of PHA resultant within the microbial cells.

Water Research, Sep 1, 2014

Titration methodologies have been used for the many years for low cost routine monitoring of full... more Titration methodologies have been used for the many years for low cost routine monitoring of full scale anaerobic digestion plants. These methodologies have been correlated to indicate the carbonate alkalinity and the volatile fatty acids (VFA) content within digesters. Two commonly used two end-point titration methods were compared using a dataset of 154 samples from energy crop and animal slurry digestates and were shown to be inaccurate in the estimation of tVFA. Using this dataset correlated with HPLC VFA analysis, two empirical bivariate linear regression equations were derived, where the validation dataset showed an absolute tVFA mean error improvement from ±3386 and ±3324 mg kg(-1) tVFA to ±410 and ±286 mg kg(-1) tVFA, respectively. The same equation was then applied to a food waste dataset where an absolute tVFA mean error was improved from ±3828 to ±576 mg kg(-1) tVFA. The newly derived titration equations can provide greater confidence in digester performance monitoring and are tools that can improve digester management.

Applied Energy, Sep 1, 2017

Environmental Technology, Aug 1, 2000

ABSTRACT

Energy & Fuels, Aug 20, 2008

Bioresource Technology, Apr 1, 2013

In this study, dielectric spectroscopy was utilised to evaluate and define the optimum harvesting... more In this study, dielectric spectroscopy was utilised to evaluate and define the optimum harvesting time for polyhydroxyalkanoates (PHA) production. It is essential to harvest PHA at the optimum time during fermentation for maximum yield, otherwise cells start degrading. Two carbon sources (acetic and butyric acids) were used in laboratory based experiments and a number of samples were measured ex situ for PHA production. The real-time measured capacitance in addition of identifying the cells growth phase, it correlated very well with ex situ measured PHA produced within the cells. The probe has proven to be a useful tool to assess process kinetics, to monitor real-time cell growth, PHA produced and defining the optimum harvesting time.

Bioresource Technology, Mar 1, 2017

Journal of Chemical Technology & Biotechnology, Oct 1, 1999

A simulated textile effluent (STE) was generated for use in laboratory biotreatment studies; this... more A simulated textile effluent (STE) was generated for use in laboratory biotreatment studies; this effluent contained one reactive azo dye, PROCION Red H-E7B (1.5 g dm−3); sizing agent, Tissalys 150 (1.9 g dm−3); sodium chloride (1.5 g dm−3) and acetic acid (0.53 g dm−3) together with nutrients and trace elements, giving a mean COD of 3480 mg dm−3. An inclined tubular anaerobic digester (ITD) was operated for 9 months on the STE and a UASB reactor for 3 months. For a 57 day period anaerobic effluent from two reactors, a UASB and an ITD, was mixed and treated in an aerobic stage. In days 77–247 68% of the true colour of PROCION Red H-E7B was removed by anaerobic treatment with no colour removal aerobically and up to 37% COD was removed anaerobically, with a corresponding BOD removal of 71%. For combined anaerobic and aerobic treatment a mean COD removal of 57% and BOD removal of 86% was achieved. Operation of the ITD at a 2.8 day HRT (volumetric loading rate (Bv) 1.24 g COD dm−3day−1) and the UASB at a 2 day HRT (Bv 1.74 g COD dm−3day−1) gave comparable COD removals but the UASB gave better true colour removal. Effluent from the combined process operating on this simulated waste still contained an average 1500 mg COD dm−3, and further treatment would be required to meet consent standards. © 1999 Society of Chemical Industry

New Biotechnology, Jul 1, 2014

Chemical Engineering Journal, Jul 1, 2016

A novel chain of processes was proposed for the first time to convert thermally hydrolysed waste ... more A novel chain of processes was proposed for the first time to convert thermally hydrolysed waste activated sludge (WAS) into concentrated volatile fatty acids (VFAs) and nutrient effluent stream for the production of biodegradable polyhydroxyalkanoates (PHAs). The integrated process involved a sequence of anaerobic fermentation followed by microfiltration (MF) and conventional electrodialysis (CED). The VFAs produced were primarily acetic and n-butyric acids, with concentrations of 3.27 and 4.37 g/L, respectively, within a total of 11.73 g/L of short chain organic acids produced from an organic loading rate of 20 g VS/L.day and 2 days hydraulic retention time anaerobic fermentation. MF achieved over 80% recovery rates of VFAs and ammonium. CED concentrated effectively the MF recovered stream with 92% of VFAs and ammonium transferred to the concentrated stream i.e.19.82 g VFAs/L (~32 g COD VFAs /L) and ammonium of 3.02 g/L. The excessive ammonium was removed through struvite precipitation before usage as substrate for PHAs production. This novel upfront process resulted in a 5 fold increase in PHA%/cell dry matter compared with the untreated thermally hydrolysed anaerobically acidified WAS stream. The results

Water Research, Apr 1, 2011

This study investigates the use of Fourier transform near infrared (FT-NIR) spectroscopy combined... more This study investigates the use of Fourier transform near infrared (FT-NIR) spectroscopy combined with principle components analysis (PCA) and partial least squares regression (PLS-R) as part of a possible process monitoring system for sewage sludge anaerobic digesters. The ability of FT-NIR with PCA to distinguish between different stages of the AD process was investigated, it was found that waste activated sludge (WAS), primary, feed (Primary:WAS 70:30) and digested sludge were distinguishable from each other using this technique. PLS-R was used successfully to track differing proportions of primary:WAS in feedstocks of 5% total solids (Coefficient of Efficiency (CE) = 0.93). The study also looked at the ability of reflectance mode NIR spectroscopy to track process parameters important for stability. Temperature and organic loading rate variations were employed to stress the digesters. Predictive models were produced for volatile fatty acids (VFA), bicarbonate alkalinity (BA) and total and volatile solids (TS and VS) and independently validated for each digester. The models were able to track the relevant process parameters: TS (CE = 0.75), VS (CE = 0.75), BA (CE = 0.71), and VFA (CE = 0.69). This technique could be used to improve the performance of sewage sludge anaerobic digesters.

Bioresource Technology, Mar 1, 2011

Waste activated sludge (WAS) is difficult to degrade in anaerobic digestion systems and pretreatm... more Waste activated sludge (WAS) is difficult to degrade in anaerobic digestion systems and pretreatments have been shown to speed up the hydrolysis stage. Here the effects of acid pretreatment (pH 6-1) using HCl on subsequent digestion and dewatering of WAS have been investigated. Optimisation of acid dosing was performed considering digestibility benefits and level of acid required. Pretreatment to pH 2 was concluded to be the most effective. In batch digestion this yielded the same biogas after 13 days as compared to untreated WAS at 21 days digestion. In semi-continuous digestion experiments (12 day hydraulic retention time at 35°C) it resulted in a 14.3% increase in methane yield compared to untreated WAS, also Salmonella was eradicated in the digestate. Dewatering investigations suggested that the acid pretreated WAS required 40% less cationic polymer addition to achieve the same cake solid content. A cost analysis was also carried out.

Energy Reports, Oct 31, 2023