Many industries in Australia and worldwide are in a situation where they produce large
quantities of wastewater which, in order to avoid human and environmental health
problems, need to be treated on site before discharge on to land or into waterways.
Appropriate treatment and disposal of waste products from abattoirs (slaughterhouses), for
example, are increasingly important due to the growing economic significance of the
market for beef products, both for export and domestic markets, and the major
environmental risks associated with these waste products. The meat processing industry is
just one example of an industry producing wastewater with very high concentrations of
suspended solids, organic matter (COD or BOD5), nitrogen and phosphorus compounds.
The potential impact of abattoir wastewater on the environment has been an area of
concern to both the industry and the public. Therefore, awareness and efforts to improve
the situation have been growing steadily. One approach to achieving a high quality effluent
is biological treatment in a combined system using anaerobic ponds in conjunction with
sequencing batch reactor (SBR) technology. This is particularly suitable for this type of
industry as it provides a very economical way to achieve effluent of tertiary treatment
standard. The anaerobic pond system can achieve substantial carbon reduction in the
wastewater before this is fed into the SBR technology. However, since a certain amount of
carbon, in particular readily biodegradable COD (RBCOD), is required to achieve
complete biological nutrient removal, the degree of pre-treatment is crucial in the success
of such a combined system. Therefore, the aim of the combined process is to reduce the
carbon content as much as possible in the anaerobic pond(s) but to have sufficient COD
remaining to enable a complete BNR process.
This dissertation presents the development of a combined anaerobic-SBR treatment
process, which, under controlled conditions, was able to achieve a high level of nutrient
removal from abattoir wastewater. Laboratory scale SBRs were fed with abattoir
wastewater with a different degree of pre-treatment in anaerobic waste stabilization ponds.
It was found that a certain degree of anaerobic pre-treatment (e.g. in anaerobic ponds) can
reduce part of the carbon concentration most efficiently while still leaving sufficient COD
required for successful biological nutrient removal (BNR).The soluble phosphorus concentration was reduced from 30-50 mg/l in the feed to < 0.5
mg/l in the effluent. The ammonium concentration was reduced from 120-160 mg/l in the
feed to < 2 mg/l in the effluent. The removal of COD, TKN, TP and SS were greater than
95%, 92%, 90% and 94%, respectively. A non-bulking sludge having a Sludge Volume
Index (SVI) of less than 100ml/g was obtained. The results show that the combination of
anaerobic pond – SBR treatment is effective in treating high strength abattoir wastewater
for carbon and nutrient removal.
Important parameters, such as COD fractions and the maximum growth rates of autotrophs
and heterotrophs, were determined using batch tests for the anaerobic ponds effluents. It
was found that some modification to determine maximum autotrophic growth is needed,
particularly for cyclic processes achieving simultaneous nitrification and denitrification.
Some experimentally determined design parameters show more variation from reported
values for domestic wastewater in abattoir wastewater. Furthermore, feed compositions
from the two anaerobic ponds were monitored (by analyzing each batch of feed) over a
four months period to determine the effect of the volatile fatty acids (VFA) concentrations
on the biological phosphorus removal performance. An additional anaerobic RBCOD test
has been developed to improve the design of the anaerobic part of bio-P removing systems.
The RBCOD value for abattoir wastewater was found to be 8% of total COD which is quite
low compared with reported values (10-20%) for raw sewage.
Simultaneous nitrification and denitrification (SND) is the process that combines
nitrification and denitrification in the same reactor (at the same time) under fully aerobic
conditions. Based on various studies, two main hypotheses, one physical and one
biological, have been proposed to explain SND. Significant research has been performed
on the biological aspects, whereas relatively little is known about the physical aspects.
This study (of physical phenomena) has also identified factors affecting simultaneous
nitrification and denitrification (SND). The main experimental studies focused on three
factors, the effect on the SND activity of soluble organic carbon, dissolved oxygen (DO)
concentrations and pH.found that the minimum required SCOD/TKN and TCOD/TKN ratios were 2.5 and
10, respectively, to achieve at least 30% of SND in abattoir wastewater. The highest SND
can be achieved through the wide range of DO control (0.3-2.0 mg/l) without affecting the
nitrification rate. SND was not affected when pH was controlled from 7.2 to 8.0 for this
Intermittent mixing in the sludge blanket during the FILL period affected the P-removal
efficiency due to contact between biomass and undiluted wastewater. However, SND
activity was not much increased.
The flexibility of the SBR configuration allowed for the development of the suitable
anaerobic/anoxic/aerobic environments necessary to ensure a good BNR performance. The
effects of various operating factors were investigated through controlled, time-oriented
operation in the cyclic period. The operation of each reactor consisted of the four basic
phases common to SBR operation: fill, react, settle and draw. These experiments sought to
understand the process behaviour and to optimize the performance. The results show that,
with this combined treatment, effluent concentrations can be achieved as low as < 2 mg/l
NH4-N, 5-10 mg/l NOx-N, < 0.5 mg/l PO4-P, 120 mg/l COD and 85-95% SND while
generating a well-settling sludge with proper process control.
The contribution of this dissertation has been the development and demonstration of a
combined treatment process to treat abattoir wastewater to achieve high nutrient removal.
The work has also focused on characterization and determination of BNR design
parameters for abattoir wastewater and to improve the understanding of the operation of
SBR processes and to demonstrate that a high degree of SND can be reliably achieved for