Nitrogen cycle of effluent-irrigated energy crop plantations:from wastewater treatment to thermo-chemical conversion processes

This paper reviews nitrogen (N) cycle of effluent-irrigated energy crop plantations, starting from wastewater treatment to thermo-chemical conversion processes. In wastewater, N compounds contribute to eutrophication and toxicity in water cycle. Removal of N via vegetative filters and specifically in short-rotation energy plantations, is a relatively new approach to managing nitrogenous effluents. Though combustion of energy crops is in principle carbon neutral, in practice, N content may contribute to NOx emissions with significant global warming potential. Intermediate pyrolysis produces advanced fuels while reducing such emissions. By operating at intermediate temperature (500°C), it retains most N in char as pyrrolic-N, pyridinic-N, quaternary-N and amines. In addition, biochar provides long-term sequestration of carbon in soils.

The microbiological destruction of thiocyanate in activated sludge plants treating coke oven effluent

The treatment of effluents produced during the manufacture of metallurgical coke is normally carried out using the activated sludge process. The efficiency of activated sludges in purifying coke oven effluent depends largely on the maintenance of species of micro-organisms which destroy thiocyanate. The composition, production, toxicity and treatment of coke oven effluent at Corby steelworks are described. A review is presented which follows the progress made towards identifying and monitoring the species of bacteria which destroy thiocyanate in biological treatment plants purifying coke oven effluents. In the present study a search for bacteria capable of destroying thiocyanate led to the isolation of a species of bacteria, identified as Pseudomonas putida, which destroyed thiocyanate in the presence of succinate; this species had not previously been reported to use thiocyanate. Washed cell suspensions of P. putida destroyed phenol and thiocyanate simultaneously and thiocyanate destruction was not suppressed by pyridine, aniline or catechol at the highest concentrations normally encountered in coke oven effluent. The isolate has been included, as N.C.I.B. 11198, in the National Collection of Industrial Bacteria, Torrey Research Station, Aberdeen. Three other isolates, identified as Achromobacter sp., Thiobacillus thioparus and T. denitrificans, were also confirmed to destroy thi.ocyanate. A technique has been developed for monitoring populations of different species of bacteria in activated sludges. Application of this technique to laboratory scale and full scale treatment plants at Corby showed that thiobacilli were usually not detected; thiobacilli were el~inated during the commissioning period of the full scale plant. However experiments using a laboratory scale plant indicated that during a period of three weeks an increase in the numbers of thiobacilli might have contributed to an improvement in plant performance. Factors which might have facilitated the development of thiobacilli are discussed. Large numbers of fluorescent pseudomonads capable of using thiocyanate were sometimes detected in the laboratory scale plant. The possibility is considered that catechol or other organic compounds in the feed-liquor might have stimulated fluorescent pseudmonads. Experiments using the laboratory scale plant confirmed that deteriorations in the efficiency of thiocyanate destruction were sometimes caused by bulking sludges, due to the excessive growth of fungal floes. Increased dilution of the coke oven effluent was a successful remedy to this difficulty. The optimum operating conditions recommended by the manufacturer of the full scale activated sludge plant at Corby are assessed and the role of bacterial monitoring in a programme of regular monitoring tests is discussed in relation to the operation of activated sludge plants treating coke oven effluents.

A dynamic model for the activated sludge treatment of coke oven effluents

This is an Inter-Disciplinary Higher Degree (IHD) thesis about Water Pollution Control in the Iron and Steel Industry. After examining the compositions, and various treatment methods, for the major effluent streams from a typical Integrated Iron and Steel works, it was decided to concentrate investigative work on the activated-sludge treatment of coke-oven effluents. A mathematical model of this process was developed in an attempt to provide a tool for plant management that would enable improved performance, and enhanced control of Works Units. The model differs from conventional models in that allowance is made for the presence of two genera of microorganisms, each of which utilises a particular type of substrate as its energy source. Allowance is also made for the inhibitive effect of phenol on thiocyanate biodegradation, and for the self-toxicity of the bacteria when present in a high substrate concentration environment. The enumeration of the kinetic characteristics of the two groups of micro-organisms was shown to be of major importance. Laboratory experiments were instigated in an attempt to determine accurate values of these coefficients. The use of the Suspended Solids concentration was found to be too insensitive a measure of viable active mass. Other measures were investigated, and Adenosine Triphosphate concentration was chosen as the most effective measure of bacterial populations. Using this measure, a model was developed for phenol biodegradation from experimental results which implicated the possibility of storage of substate prior to metabolism. A model for thiocyanate biodegradation was also developed, although the experimental results indicate that much work is still required in this area.

A method for the in-situ determination of the hydraulic conductivity of gravels as used in constructed wetlands for wastewater treatment

A new instrument and method are described that allow the hydraulic conductivities of highly permeable porous materials, such as gravels in constructed wetlands, to be determined in the field. The instrument consists of a Mariotte siphon and a submersible permeameter cell with manometer take-off tubes, to recreate in-situ the constant head permeameter test typically used with excavated samples. It allows permeability to be measured at different depths and positions over the wetland. Repeatability obtained at fixed positions was good (normalised standard deviation of 1–4%), and results obtained for highly homogenous silica sand compared well when the sand was retested in a lab permeameter (0.32 mm.s–1 and 0.31 mm.s–1 respectively). Practical results have a ±30% associated degree of uncertainty because of the mixed effect of natural variation in gravel core profiles, and interstitial clogging disruption during insertion of the tube into the gravel. This error is small, however, compared to the orders of magnitude spatial variations detected. The technique was used to survey the hydraulic conductivity profile of two constructed wetlands in the UK, aged 1 and 15 years respectively. Measured values were high (up to 900 mm.s –1) and varied by three orders of magnitude, reflecting the immaturity of the wetland. Detailed profiling of the younger system suggested the existence of preferential flow paths at a depth of 200 mm, corresponding to the transition between more coarse and less coarse gravel layers (6–12 mm and 3–6 mm respectively), and transverse drift towards the outlet.

Characteristics of the upper phase of bio-oil obtained from co-pyrolysis of sewage sludge with wood, rapeseed and straw

Sewage sludge was pyrolysed with 40% mixed wood, 40% rapeseed and 40% straw. The reason for the mixture of different biomass is to investigate the impact of co-pyrolysis on the upper phase of bio-oil in terms of changes to composition, elemental analysis, viscosity, water content, pH, higher heating value and acid number that could impact on their applications. The biomass was pyrolysed in a laboratory at 450 °C and bio-oil was collected from two cooling traps. The bio-oil obtained from co-pyrolysis of sewage sludge with wood, rapeseed and straw was analysed for composition using the gas chromatography mass spectrometry. The upper phase from the co-pyrolysis process was also characterised for ultimate analysis, higher heating values, water content, viscosity, pH and acid number. There was an increase in the amount of upper phase produced with co-pyrolysis of 40% rapeseed. It was also found that the upper phase from sewage sludge with mixed wood has the highest viscosity, acid number and lowest pH. The bio-oil containing 40% straw was found to have a pH of 6.5 with a very low acid number while the 40% rapeseed was found to have no acid number. Sewage sludge with 40% rapeseed was found to have the highest energy content of 34.8 MJ/kg, 40% straw has 32.5 MJ/kg while the 40% mixed wood pyrolysis oil has the lowest energy content of 31.3 MJ/kg. The 40% rapeseed fraction was found to have the highest water content of 8.2% compared to other fractions.

The intermediate pyrolysis of de-inking sludge to produce a sustainable liquid fuel

De-inking sludge is a waste product generated from secondary fibre paper mills who manufacture recycled paper into new paper sheets; it refers directly to the solid residues which evolve during the de-inking stage of the paper pulping process. The current practice for the disposal of this waste is either by land-spreading, land-filling or incineration which are unsustainable. This work has explored the intermediate pyrolysis of pre-conditioned de-inking sludge pellets in a recently patented 20 kg/h intermediate pyrolysis reactor (The Pyroformer). The reactor is essentially two co-axial screws which are configured in such a way as to circulate solids within the reactor and thus facilitate in the cracking of tars. The potential application of using the volatile organic vapours and permanent gases evolved would be to generate both combined heat and power (CHP) located at paper making sites. The results show that de-inking sludge could be successfully pyrolysed and the organic vapours produced were composed of a mixture of aromatic hydrocarbons, phenolic compounds and some fatty acid methyl esters as detected by liquid GC-MS. The calorific value of the oil after condensing was between 36 and 37 MJ/kg and the liquid fuel properties were also determined, permanent gases were detected by a GC-TCD and were composed of approximately 24% CO, 6% CH and 70% CO (v/v%). The solid residue from pyrolysis also contained a small residual calorific value, and was largely composed of mainly calcium based inert metal oxides. The application of applying intermediate pyrolysis to de-inking sludge for both CHP production and waste reduction is in principle a feasible technology which could be applied at secondary fibre paper mills. © 2013 Elsevier B.V. All rights reserved.