D. A. J. Wase

Continuous co-digestion of cattle slurry with fruit and vegetable wastes and chicken manure

Abstract Anaerobic digestion is a well established process for treating many types of organic waste, both solid and liquid. As such, the digestion of cattle slurries and of a range of agricultural wastes has been evaluated and has been successful. Previous batch studies have shown that based on volatile solids (VS) reduction, total methane production and methane yield, co-digestions of cattle slurry (CS) with fruit and vegetable wastes (FVW) and with chicken manure (CM) were among the more promising combinations. A continuously stirred tank reactor ( 18 litres ) was used as a mesophilic (35°C) anaerobic reactor to examine the effect of adding the FVW and CM to a system which was digesting CS. The retention time was kept at 21 days and the loading rate maintained in the range 3.19– 5.01 kg VS m −3 d −1 . Increasing the proportion of FVW from 20% to 50% improved the methane yield from 0.23 to 0.45 m 3 CH 4 kg −1 VS added, and caused the VS reduction to decrease slightly. Increasing the proportion of chicken manure in the feed caused a steady deterioration in both the criteria for judging digester performance. This appeared to be caused by ammonia inhibition.

Co-digestion of waste organic solids: batch studies

Anaerobic digestion is a well established process for treating many types of organic waste, both solid and liquid. As such, the digestion of cattle slurries and of the organic fraction of municipal solid waste has been evaluated and has been successful. Attempts to apply the process to other types of solid organic waste, for example, to chicken manure, have met with limited success. In many areas of the UK, intensive chicken farming is leading to solids disposal problems. It has been proposed that co-digestion with cattle slurry could be a possible disposal route for chicken manure. In this study, cattle slurries were mixed with a range of solid wastes and allowed to digest in 1-1 batch digesters. The criteria for judging the success of a co-digestion were volatile solids (VS) reduction, total methane production and methane yield. In terms of the VS reductions (%), there was little difference between the various digestions. In terms of the cumulative methane production (1) the co-digestions with fruit and vegetable waste, the fish offal and the dissolved air flotation sludge were more effective than the digestion with cattle slurry alone. In terms of the specific methane yield (m3 CH4 kg−1 VS removed), the co-digestions containing fish offal and the brewery sludge gave higher values than the control digestion with cattle slurry alone. Compared with their control (cattle slurry alone), both co-digestions with poultry manure (7.5 and 15% TS) gave higher cumulative productions of methane and the system with the lower concentration of poultry manure gave a higher specific methane yield. However, there was some evidence of ammonia inhibition.

Production of α-amylase by Bacillus amyloliquefaciens in batch and continuous culture using a defined synthetic medium

SummaryUsing a totally defined synthetic medium the effect of lactose and nitrogen on cell physiology and α-amylase production by Bacillus amyloliquefaciens B155 were investigated. Results showed cell growth and α-amylase production patterns to be similar regardless of the limiting nutrient and suggested stationary phase gene control of α-amylase production as opposed to a direct response to nutrient limitation.

Instability of α-amylase production and morphological variation in continuous culture of Bacillus amyloliquefaciens is associated with plasmid loss

Continuous cultivation of Bacillus amyloliquefaciens B155 using a defined synthetic medium, which supports good batch cell growth and α-amylase production, was limited by lactose, nitrogen, phosphorus and oxygen. In each case, the organism changed to a non-α-amylase-producing variant with morphological characteristics different from the original culture. Reinitiation of α-amylase production could not be achieved by plating the variant culture on solid complex medium. α-Amylase-producing and non-α-amylase-producing colonies, isolated from nitrogen-limited continuous culture were tested for plasmid DNA. The α-amylase-producing cells contained plasmid DNA, whereas non-α-amylase-producing cells did not. This suggests that plasmid structural instability (resulting in plasmid DNA loss or plasmid copy number reduction by metabolic control) accompanies loss of α-amylase production by B. amyloliquefaciens during continuous fermentations.

AN EXAMINATION OF THE CONTINUOUS ANAEROBIC CO-DIGESTION OF CATTLE SLURRY AND FISH OFFAL

A continuously stirred tank reactor (18 l) was used as an anaerobic reactor to examine the effect of adding fish offal to a system which was digesting cattle slurry. The retention time was kept at 21 days and the loading rate maintained in the range 5.1 – 6.3 kg volatile solids (VS) m −3 d −1 . 4% (w/w) fish offal caused some deterioration in the performance of the digester, judged in terms of both the VS reduction and methane yield. 6% fish offal caused a significant disruption in the digester’ s performance. The concentrations of free ammonia which were present in the liquors tended to decrease when the fish offal was present and did not exceed 100 mgl −1 . This is below the concentrations which have previously been shown to be inhibitory. Volatile fatty acid concentrations increased during the additions of the fish offal. Taken in conjunction with the high fat/oil concentration of the fish offal, it was considered that long chain fatty acids were the most likely cause of the digester failure.

Rearrangement of lactose on sterilization

SummaryThermal sterilisation of a lactose-based medium resulted in rearrangement of substantial amounts of lactose to lactulose which was not fermented.

Mixing characteristics of fixed film anaerobic reactors

SummarySince the mixing characteristics of anaerobic reactors would appear to have an effect on their operational performance, lithium tracer studies were made on two different digester types; the upflow sludge blanket and the expanded bed reactors. The mixing characteristics of both types of reactor, defined by this technique, were found to be of the intermediate type with a bias towards good mixing.

A short note on anaerobic digestion of apples

ConclusionsWe conclude that apples are readily converted to biogas by anaerobic digestion. Of the three stages, gas production, digestibility and solids handling, it is likely that the limiting factor would be solids handling.

Separation of polymer from activated sludge

SummaryA simple large-scale method of separating polymer from activated sludge by shear, using a continuous centrifuge, is given.

Two chemically defined media for the growth of Acholeplasma laidlawii strain A

A total of 11 tissue culture media and one synthetic medium were screened to determine whether they could support the growth of two strains of Acholeplasma. Two similar chemically defined media were found in which Acholeplasma laidlawii Strain A (Buchanan & Gibbons 1974) could grow. This is the first report of a fully defined medium for the growth of this organism (Greenaway 1981).