Richard M. Dinsdale

Sustainable fermentative hydrogen production: challenges for process optimisation

Abstract This paper reviews information from continuous laboratory studies of fermentative hydrogen production useful when considering practical applications of the technology. Data from reactors operating with pure cultures and mixed microflora enriched from natural sources are considered. Inocula have been derived from heat-treated anaerobically digested sludge, activated sludge, aerobic compost and soil, and non-heat-treated aerobically composted activated sludge. Most studies are on soluble defined substrates, and there are few reports of continuous operation on complex substrates with mixed microflora to produce H2. Methanogenesis which consumes H2 may be prevented by operation at short hydraulic retention times (around 8– 12 h on simple substrates) and/or pH below 6. Although the reactor technology for anaerobic digestion and biohydrogen production from complex substrates may be similar, there are important microbiological differences, including the need to manage spore germination and oxygen toxicity on start-up and control sporulation in adverse circumstances during reactor operation.

The occurrence of pharmaceuticals, personal care products, endocrine disruptors and illicit drugs in surface water in South Wales, UK

The presence and fate of 56 pharmaceuticals, personal care products, endocrine disruptors and illicit drugs (PPCPs) were investigated in the South Wales region of the UK. Two contrasting rivers: River Taff and River Ely were chosen for this investigation and were monitored for a period of 10 months. The impact of the factors affecting the levels of concentration of PPCPs and illicit drugs in surface water such as surrounding area, proximity to wastewater effluent and weather conditions, mainly rainfall was also investigated. Most PPCPs were frequently found in river water at concentrations reaching single microgL(-1) and their levels depended mainly on the extent of water dilution resulting from rainfall. Discharge of treated wastewater effluent into the river course was found to be the main cause of water contamination with PPCPs. The most frequently detected PPCPs represent the group of pharmaceuticals dispensed at the highest levels in the Welsh community. These were antibacterial drugs (trimethoprim, erythromycin-H(2)O and amoxicillin), anti-inflammatories/analgesics (paracetamol, tramadol, codeine, naproxen, ibuprofen and diclofenac) and antiepileptic drugs (carbamazepine and gabapentin). Only four PPCPs out of 56 (simvastatin, pravastatin, digoxin and digoxigenin) were not quantified over the course of the study. Several PPCPs were found to be both ubiquitous and persistent in the aqueous environment (e.g. erythromycin-H(2)O, codeine, carbamazepine, gabapentin and valsartan). The calculated average daily loads of PPCPs indicated that in total almost 6 kg of studied PPCPs are discharged daily into the studied rivers. The illicit drugs studied were found in rivers at low levels of ng L(-1). Average daily loads of amphetamine, cocaine and its main metabolite benzoylecgonine were as follows: 8, 1.2 and 39 gday(-1), respectively. Their frequent occurrence in surface water is primarily associated with their high illegal usage and is strongly associated with the discharge of insufficiently treated wastewater effluent.

Enhancement of hydrogen production from glucose by nitrogen gas sparging

The effect on hydrogen yield of N2 sparging was investigated in non-sterile conditions using a hydrogen-producing mixed culture previously enriched from soya bean meal. A continuous stirred-tank reactor (CSTR) at 35°C and pH 6.0 was operated on a mineral salts-glucose (10 g l−1) medium at a hydraulic retention time (HRT) of 8.5 h, and organic loading rate of 27.02 g glucose litre reactor−1 day−1. Results are reported from an 8 week period of continuous operation, and the enrichment culture gave stable results over an extended period. A hydrogen yield of 0.85 moles H2/mole glucose consumed was obtained after 5 HRT, the gas produced being 53.4% H2. With N2 sparging at a flow rate approximately 15 times the hydrogen production rate, the hydrogen yield was 1.43 moles H2/mole glucose consumed. The specific hydrogen production rate increased from 1.446 ml hydrogen min−1g−1 biomass to 3.131 ml hydrogen min−1 g−1 biomass under sparging conditions. It is suggested that hydrogen partial pressure in the liquid phase was an important factor affecting hydrogen yield. Energy could be recovered as hydrogen from processes generating volatile fatty acids for fine chemicals and liquid bio-fuels or from acidification reactors preceding normal anaerobic biological treatment of sugary wastewaters.

The effect of signal suppression and mobile phase composition on the simultaneous analysis of multiple classes of acidic/neutral pharmaceuticals and personal care products in surface water by solid-phase extraction and ultra performance liquid chromatography–negative electrospray tandem mass spectrometry

A new multi-residue method for the determination of 25 acidic/neutral pharmaceuticals (antibiotics, anti-inflammatory/analgesics, lipid regulating agents, diuretics, triazides, H2-receptor antagonists, cardiac glicozides and angiotensin II antagonists) and personal care products (sunscreen agents and preservatives) in surface water with the usage of a new technique: ultra performance liquid chromatography-negative electrospray tandem mass spectrometry (UPLC-MS/MS) was developed and validated. The novel UPLC system with 1.7 microm particle-packed column allowed for good resolution of analytes with the application of low mobile phase flow rates (0.05 mL min(-1)) and short retention times (from 4.7 min to 13.3 min) delivering a fast and cost-effective multi-residue method. SPE with the usage of Oasis MCX strong cation-exchange mixed-mode polymeric sorbent was chosen for sample clean-up and concentration. The influence of mobile-phase composition, matrix assisted ion suppression and SPE recovery on the sensitivity of the method was identified and quantified. The instrumental limits of quantification varied from 0.2 microgL(-1) to 30mugL(-1). The method limits of quantification were at low nanogram per litre levels and ranged from 0.3 ng L(-1) to 30 ng L(-1). The instrumental and method intra-day and inter-day repeatabilities were on average less than 5%. The method was successfully applied for the determination of PPCPs in River Taff. Thirteen compounds were determined in river water at levels ranging from a single to a few hundred nanograms per litre. Among them were ten pharmaceuticals (aspirin, salicylic acid, ketoprofen, naproxen, diclofenac, ibuprofen, mefenamic acid, furosemide, sulfasalazine and valsartan) and three personal care products (methyl- and ethylparaben and 4-benzophenone).

The effect of acid pretreatment on the anaerobic digestion and dewatering of waste activated sludge

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.

Illicit drugs and pharmaceuticals in the environment – Forensic applications of environmental data. Part 1: Estimation of the usage of drugs in local communities

Pharmaceuticals and recently also illicit drugs have been recognised as emerging environmental contaminants due to their potential environmental impact: frequent occurrence, persistence and risk to aquatic life and humans. This manuscript is part one of the two-part study aiming to provide a better understanding and application of environmental data not only for environmental aims but also to meet forensic objectives. An attempt to use wastewater data is made in order to verify patterns of the usage of drugs (in particular illicit) in local communities. The average usage of cocaine in South Wales was estimated at 0.9 g day(-1) 1000 people(-1), which equals 1 tonne of this drug used or disposed of to sewage annually in Wales. The calculated usage of amphetamine denoted 2.5 g day(-1) 1000 people(-1) and is suspected to be an overestimate. Because no analysis of enantiomers of amphetamine was undertaken, no distinction between amphetamines legal and illicit usage could be made.

Modular tubular microbial fuel cells for energy recovery during sucrose wastewater treatment at low organic loading rate.

Energy recovery while treating low organic loads has been investigated using longitudinal tubular microbial fuel cell (MFC) reactors. Duplicate reactors, each consisting of two modules, were operated with influent sucrose organic loading rates (OLRs) between 0.04 and 0.42 g COD/l/d. Most soluble COD (sCOD) removal occurred in the first modules with predominantly VFAs reaching the second modules. Coulombic efficiency (CE) in the second modules ranged from 9% to 92% which was 3-4 times higher than the first modules. The maximum energy production was 1.75 W h/g COD in the second modules at OLR 0.24 g/l/d, up to 10 times higher than the first modules, attributable to non-fermentable substrate. A simple plug flow model of the reactors, including a generic non-electrogenic reaction competing for acetate, was developed. This modular tubular design can reproducibly distribute bioprocesses between successive modules and could be scalable, acting as a polishing stage while reducing energy requirements in wastewater treatment.

Development of a static headspace gas chromatographic procedure for the routine analysis of volatile fatty acids in wastewaters.

An optimised procedure has been developed for the routine analysis of volatile fatty acids in wastewater matrices, using static headspace gas chromatography with flame ionisation detection. Factors such as sample volume, sample pre-treatment and the time and temperature of sample equilibration have been included in an optimisation model designed to provide maximum detector response for acetic, propionic, iso- and n-butyric and iso- and n-valeric acids in the concentration range 0-1000 mg/l. Optimal headspace conditions were observed when equilibrating at 85 degrees C for 30 min, using a 2.0 ml sample volume with the addition of 1.0 ml of NaHSO4 (62%, w/v) into standard 22.3 ml vials. 2-Ethylbutyric acid was used as an internal standard. The suitability of ordinary least squares regression and weighted least squares regression models for the purposes of calibration and quantification were investigated. A weighted least squares linear regression model applied to the heteroscedastic data provided lower detection limits, e.g. 3.7 and 3.3 mg/l for acetic and propionic acids.

Life cycle assessment of biogas infrastructure options on a regional scale

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.

Fermentative biohydrogen production systems integration

Acidogenic fermentation can be used to produce hydrogen from a range of biomass sources. The effluent from this process can be utilised in a number of biological processes enabling further recovery of energy from the biomass. In this review a number of candidate technologies are assessed including conventional methanogenic anaerobic digestion, dark fermentative hydrogen production, photo-fermentation, and bioelectrochemical systems. The principles, benefits and challenges associated with integrating these technologies are discussed, with particular emphasis on integration with fermentative hydrogen production, and the current state of integrative development is presented. The various system configurations for potential integrations presented here may simultaneously permit an increase in the conversion efficiency of biomass to energy, improved adaptability to varying operating conditions, and improved stability. Such integration, while increasing system complexity, may mean that these bioprocesses could be deployed in a wider range of scenarios and be used with a greater range of substrates.