Andrew D. Wheatley

The toxicity of textile reactive azo dyes after hydrolysis and decolourisation

The toxicity of C.I. Reactive Black 5 and three Procion dyes, as found in textile effluents, was determined using the bioluminescent bacterium Vibrio fischeri. Hydrolysed Reactive Black had a slightly greater toxicity than the parent form (EC(50) 11.4+/-3.68 and 27.5+/-4.01 mg l(-1), respectively). A baffled bioreactor with anaerobic and aerobic compartments was used to decolourise hydrolysed Reactive Black 5 in a synthetic effluent. Decolourisation of hydrolysed Reactive Black resulted in an increased toxicity (EC(50) 0.2+/-0.03 mg l(-1)). Toxicity was not detectable when decolourised Reactive Black 5 was metabolised under aerobic conditions. No genotoxicity was detected after the decolourisation of either the parent or the hydrolysed reactive dyes, either in vitro or in the bioreactor. The toxicity and genotoxicity of decolourised C.I. Acid Orange 7 was due to the production of 1-amino-2-naphthol (EC(50) 0.1+/-0.03 mg l(-1)).

Anaerobic/aerobic treatment of coloured textile effluents using sequencing batch reactors

Conventional biological wastewater treatment plants do not easily degrade the dyes and polyvinyl alcohols (PVOH) in textile effluents. Results are reported on the possible advantages of anaerobic/aerobic cometabolism in sequenced redox reactors. A six phase anaerobic/aerobic sequencing laboratory scale batch reactor was developed to treat a synthetic textile effluent. The wastewater included PVOH from desizing and an azo dye (Remazol Black). The reactor removed 66% of the applied total organic carbon (load F: M 0.15) compared to 76% from a control reactor without dye. Colour removal was 94% but dye metabolites caused reactor instability. Aromatic amines from the anaerobic breakdown of the azo dyes were not completely mineralised by the aerobic phase. Breakdown of PVOH by the reactor (20-30%) was not as good as previous reports with entirely aerobic cultures. The anaerobic cultures were able to tolerate the oxygen and methane continued to be produced but there was a deterioration in settlement.

Hydrothermal carbonisation of sewage sludge: effect of process conditions on product characteristics and methane production.

Hydrothermal carbonisation of primary sewage sludge was carried out using a batch reactor. The effect of temperature and reaction time on the characteristics of solid (hydrochar), liquid and gas products, and the conditions leading to optimal hydrochar characteristics were investigated. The amount of carbon retained in hydrochars decreased as temperature and time increased with carbon retentions of 64-77% at 140 and 160°C, and 50-62% at 180 and 200°C. Increasing temperature and treatment time increased the energy content of the hydrochar from 17 to 19 MJ/kg but reduced its energy yield from 88% to 68%. Maillard reaction products were identified in the liquid fractions following carbonisations at 180 and 200°C. Theoretical estimates of the methane yields resulting from the anaerobic digestion of the liquid by-products are also presented and optimal reaction conditions to maximise these identified.

The anaerobic filtration of dairy waste: Results of a pilot trial

Results are presented from a pilot scale (4·3 m3) upflow anaerobic filter for the treatment of the wastewater from ice-cream manufacture. The reactor was completely mixed by gas production but the solids or sludge held within the reactor were shown to be affected by the liquid velocities. The reactor was subject to a number of organic and hydraulic shocks and this reduced the consistency of COD removal. Daily loading rates varied from 0 to 18 kg COD/m3/day but with an average load of 5·5 kg/m3/day the mean COD removal was 70%. This was compared with previous work and shown to be a typical performance for an anaerobic filter. Alkalinity and carboxylic acid data are also presented and were within the normal, stable, operating range. Previous research on the anaerobic treatment of industrial effluents has shown alkalinity to be the most important factor controlling reliability.

The impact of Local Authorities’ interventions on household waste collection: A case study approach using time series modelling

At a local Government level there have been many interventions and changes made to household waste collection services to meet new regulatory requirements. These changes include separate collection of recyclable and organic materials. This paper has used a time series model to quantify the success of interventions introduced by a LA. The case study was a medium sized UK LA, Charnwood Borough Council (CBC), the research analyses monthly data of quantities of recyclates, garden waste for composting and residual waste for landfill disposal. The time series model was validated with a five year data set and used to measure the impacts of the various changes to identify which intervention was the most successful, while controlling for season and number of working days. The results show the interventions analysed both had abrupt and permanent positive impacts on the yield of recyclable materials, and a corresponding negative impact on the residual waste. The model could be added to the National data base to help LAs to compare interventions and to understand which schemes encourage householder participation and improve recycling performance.

Leaching of Trace Metals from Two Different Size Soils

Two different size-grained soils were subjected to column experiments with a hydraulic loading representing two years’ rainfall. Leachates were collected and analysed for pH and temperature and for eight trace metals, namely; Iron (Fe), Copper (Cu), Chromium (Cr), Nickel (Ni), Lead (Pb), Manganese (Mn), Zinc (Zn), and Silica (Si). The analysis was conducted using an inductively coupled plasma (ICP) method of spectrometry. The results show different extractable metal concentrations from the two soil samples.

A Comparison of Ammonia Measurements Using Fourier Transform Infrared and Tuneable Diode Laser Spectroscopy

Current diesel engine after-treatment systems such as Selective Catalyst Reduction (SCR) use ammonia (NH3) to reduce Nitrogen Oxides (NOx) into Nitrogen (N2) and water. However, if the reaction between NH3 and NOx is unbalanced, it can lead either to NH3 or NOx being released into the environment. As NH3 is classified as a hazardous compound on the environment, its accurate measurement is essential.Fourier Transform Infrared (FTIR) and Tuneable Diode Laser (TDL) spectroscopy are two of the methods that can measure raw emissions from engine exhaust pipes, especially NH3. However, it is difficult to suggest which method is the right one for measuring NH3 from engine exhausts.This paper compares the effectiveness of FTIR and TDL methods for NH3 measurement from diesel engine exhausts, based on tests conducted under well-controlled laboratory conditions. The concentration of NH3 from a diesel engine was measured under both a steady-state test cycle and a transient test cycle. The NH3 readings from FTIR and TDL were analysed, for comparison of precision, response time and their accuracy. It was shown that both techniques were suitable with attention to the different sampling procedures to avoid absorption.Copyright

Community scale, decentralised anaerobic digestion for energy and resource recovery

The paper describes “Community scale, decentralized anaerobic digestion for energy and resource technology” which is a joint UK-Thailand project much in line with the current aims of the Thai Government for decentralized energy generation. The use of food waste for biogas generation by the process of anaerobic digestion provides multiple benefits: decreased energy dependency, nutrient preservation and recycling, and reduced greenhouse gas emissions. It is also promoted in the remoter Scotland and Wales of the UK. The aim of the project is the design and deployment of small scale digesters and their networking into remotely monitored units. Here, we are describing initial design of the reactors and some issues associated with using food waste as substrate. Based on the literature, we have also estimated the reactors performance to be 0.40-0.50 m3/kg of feedstock for biogas production.

The behaviour of metal contaminants in silty sand and gravel

An investigative study is reported to determine the behaviour of metal contaminants in silty sand and gravel. A soil box experiment was conducted with a silty sand of permeability, k = 3.9242x10-5 m/s. The sand was placed on a bedding of 6 mm peagravel, inside the test box. Copper Nitrate, Chromium Nitrate, Nickel Sulphate and Lead Nitrate were dissolved, mixed with RO (reverse osmosis) water for use in four separate experiments. Column tests were conducted with the same silty sand and gravel and under similar experimental conditions. Copper flushing was very slow, it was strongly absorbed to the silty sand and gravel. Chromium was entirely retained (34mg/Kg) within the experimental system, and its released concentrations were very low. Nickel was shown to have a good aqueous solubility thus it was freely mobile in the sand. There was some minor adsorption of Nickel though lower than that of Copper and Chromium.

Operational experiences of industrial scale AD: Lessons for the future

In this paper we discuss operational experiences of two large industrial anaerobic digestion facilities processing brewery waste and maize. The raw effluent from the brewery waste has COD ranging from 5500 mg/l to 41400 mg/l, with variable flow rate and suspended solids up to 4800 mg/l. The Anaerobic Digestion (AD) treatment uses 900m3 EGSB reactor. The two-year monitoring of data includes Ripleys Ratio, Volatile Fatty Acids, and pH. These parameters indicate lower performance and certain instability before the planned maintenance works, followed by the much improved performance afterwards. The average biogas production is 3540 Nm3/day but the variance of the biogas flow remains an issue. The combined Heat and Power (CHP) production from energy crops uses ensilaged, purposely grown maize with 28-34% dry matter and chop length of 6-9 mm. The available three-year data for this AD facilities indicate great process stability. It uses 150 t/day of maize, and result in energy production of 21 GW/year which is 7000 homes equivalent. This energy is evenly split between the sewage treatment works and injection to the public electricity grid. Depending on the dry solids content, the digestate is either stored and spread on the land, or sold to farmers.