Conference Papers | 2002 Conference Papers
REMOVAL USING 'MLE' PROCESS - EXPERIENCES AT BALLARAT
David Reyne, Plant
Operator Wastewater Treatment, Central
Ballarat North Wastewater Treatment Plant is one of
the few Victorian plants remaining that discharge secondary
class effluent to inland waters. With recent changes
to the existing EPA discharge licence, Ammonia and Total
Nitrogen limits have been set such that the traditional
biological trickling filters struggle to achieve. To
this end Central Highlands Water has been investigating
a number of options to achieve compliance. It was decided
to design and build a small pilot plant using an activated
sludge process in the Modified Ludzack-Ettinger configuration,
which has subsequently produced encouraging results.
Having a high proportion of trade waste in the influent,
CHW then decided to duplicate the pilot plant and test
the process on a single industrial source, which has
high ammonia concentrations. The pilot systems have
successfully met ammonia removal efficiencies in excess
of 95% and concentrations of less than 1.0 mg/L.
Modified Ludzak-Ettinger (MLE), Ballarat North Wastewater
Treatment Plant (BNTP), 'a' Recycle, Biological Trickling
Filters (BTF), Mixed Liquor Suspended Solids (MLSS).
North Wastewater Treatment Plant (BNTP) was designed
and built in the 1960s and consists of a conventional
secondary treatment process using primary treatment,
biological trickling filters and final clarification.
Over the years minor upgrades have been made to improve
plant performance such as chemically dosing to reduce
phosphorus concentrations. BNTP receives trade waste
from the largest customers of the Authority, with the
organic load from these contributors accounting for
about 70% of the total load on the plant.
Highlands Water has plans to augment the Ballarat North
plant over the next few years. However the existing
plant currently suffers from extreme overload conditions
brought about by an expanding catchment load and also
a high industrial discharge from a number of sources.
Therefore a need was established to investigate what,
if any, interim options were available to CHW to achieve
the Licence requirements for a short-term period.
scope of the investigations was to determine works that
were necessary for short term compliance with the existing
EPA discharge requirements, keeping in mind the longer
term objectives of the plant. Thus an interim solution
was sought to meet the enforced targets until the major
augmentation under 'SmartCycle' is commissioned towards
the end of 2005.
In order to reduce the ammonia and also the total nitrogen
leaving the plant, additional nitrification/ denitrification
capacity at the plant was required. To this end a decision
was made to pursue the potential for a high rate activated
sludge solids contact process to be added to the existing
BTF to treat part or the entire flow stream.
principle is based on the BTF continuing to produce
the current filtrate quality and part or all of this
filtrate stream then being directed to the solids contact
process to effect additional nitrification. If an anoxic
zone or an intermittent operation of the aeration cycle
is incorporated, this would assist in delivering denitrification
which would reduce the nitrates and in turn reduce the
total nitrogen leaving the process.
Because of the significant and strong trade waste component,
it was decided to proceed as follows:
Prove the ability of the waste to flocculate by firstly
establishing a basic activated sludge process train;
If 1 was successful, trial the MLE process on Settled
Sewage with its additional carbon source;
trial the MLE process on various blends of Filtrate
+ Settled Sewage.
primary objective was to establish how well the MLE
process in series with the biological trickling filtration
plant, could nitrify and denitrify the Ballarat North
raw sewage. A secondary objective was to establish just
how low a sludge age (SRT) the process could successfully
be operated at bearing in mind the very low sewage temperature.
initial attempt at the pilot plant utilized two tanks,
one for aeration and one for clarification. Also a smaller
drum was used as wet well for the Return Activated Sludge
(RAS) to be pumped back to the aeration tank via a small
submersible pump. Air was supplied by a small blower
through four 6" stone diffusers.
the pilot study was to be conducted using filtrate from
the BTF plant. However the biomass was slow to develop,
and this was attributed to the C:N:P ratio of the filtrate
being around 3.3:4.6:1. Seeding with RAS from the Ballarat
South Treatment Plant (BSTP) was commenced and introduced
into the pilot plant RAS wet well. This seeding process
was repeated over several days with little success.
Given the slow progress it was decided to switch from
filtrate to settled sewage with a more optimal C:N:P
ratio of 10:4.6:1. Once this configuration started building
biomass with intense seeding from BSTP, some good results
were achieved with an 80% reduction in Ammonia in a
couple of grab samples which gave some confidence in
this overall initial period, there was little success
due to major mechanical problems. This manifested itself
causing difficulties in keeping solids in the systems
and other issues. During this phase, numerous practical
problems were experienced, such as difficulty in adjusting
the MLSS flow to the clarifier without disturbing the
sludge blanket and floc shearing through pumping. Perhaps
the most significant operational problem was the inability
to concentrate solids and then remove the settled solids
from the two flat-bottomed clarifiers. To overcome this
problem a single coned shape plastic tank was installed
to act as a clarifier.
these initial practical problems were resolved, and
although the plant consisted of the most basic activated
sludge configuration, the pilot plant was clearly demonstrating
significant nitrification and denitrification. Thus
the suitability of the activated sludge process albeit
in a basic conventional mode and using settled sewage,
way forward from this point was to achieve a stable
process for nitrification and denitrification. Consequently
the incorporation of a denitrification step within the
process was required. In this case a separate anoxic
zone was needed and the Modified Ludzack-Ettinger (MLE)
process was chosen as the way forward. Figure 1 and
2 shows the flow schematic of the MLE process and a
picture of the MLE pilot plant.
1: Modified Ludzack-Ettinger Pilot Plant
Figure 2: Pilot Plant located at Ballarat North Wastewater
For a period the Pilot Plant was operated in a (MLE)
process configuration at a sludge age (SRT) of 10 days.
The SRT was known precisely by virtue of wasting a fixed
flow-monitored quantity of MLSS each day. The changing
of mode to the MLE process involved adding an anoxic
zone and a recycle line from the aeration zone back
to the anoxic zone'a' recycle or 'NML' (nitrified mixed
liquor ) recycle.
run in the MLE mode with settled sewage as the feed
for some days, the target MLSS was reached and wasting
from the system began. Initially wasting from the RAS
line was chosen. This proved to give operational problems
with scum and rising sludge and it was difficult to
maintain an accurate assessment of the SRT with consequent
loss of control. To overcome this, wasting was changed
to the aeration tank to give better control over MLSS.
The change in method produced excellent results with
ammonia reductions of >90%. These results were continuously
achieved over the following months with ammonia levels
reducing by 99% consistently.
In order to achieve the initial aim of treating BTF
filtrate through an additional process, the feed for
the pilot was changed to give a 50:50 blend of filtrate
and settled sewage. Settled sewage was added to the
filtrate as a carbon source to aid in the process, especially
for denitrification. The blend was then subsequently
modified again to a 25:75 settled sewage/filtrate blend
to push the system a little harder. Some modifications
were made to the recycle rates and this process, once
stabilised, also achieved an excellent reduction in
ammonia. With the reduced proportion of settled sewage
in the feed to the pilot plant, predictably denitrification
suffered. Rather than continue and incorporate a larger
denitrification zone, it was at this point that the
trials were concluded.
clearly, the trials proved that:
Whilst the Ballarat North raw sewage is very strong
with a 70% industrial component, the MLE activated
sludge process is extremely effective in reducing
TKN in the settled sewage from around 80.0mg/L to
<<1.0mg/L and TN < 10.0 mg/L.
MLE activated sludge process is very robust and repeatable.
treating low sewage temperatures, the activated sludge
process performs extremely well at very low SRTs.
Significant analysis of the waste was completed together
with analysis of flow regimes, recycle rates, WAS rates,
RAS rates and sludge age. The design and modelling for
this project was undertaken by Zemek Environmental Pty
Ltd. The model predictions were very close to the actual
results analysed in the field. The pilot produced excellent
results with significant reductions in BOD, phosphorus,
ammonia and nitrate. Graph 1 depicts the levels of ammonia
in the feed and the concentration leaving the process
for pilot plant using the settled sewage as the only
Graph 1: BNTP Pilot Plant -
MLE Settled Sewage
this period the pilot plant performed extremely well.
Typically the pilot plant designed as a MLE process
without any detailed consideration to its design for
bio-P removal, has produced the following results:
Ammonia - < 4.0 mg/L (the initial testing apparatus
was limited to a minimum reading of 4.0mg/L however
based on CHW laboratory results this value was typically
< 1.0 mg/L)
Nitrogen ~ < 10.0 mg/L
phosphorus ~ < 0.6 mg/L
Graphs 2 and 3 depict outcomes gained by using a combined
feed of settled sewage and biological trickling filter
filtrate. As shown the pilot performed very well with
significant reductions, up 99%, in ammonia concentrations.
2: BNTP Pilot Plant - MLE 50% Settled Sewage : 50% BTF
3: BNTP Pilot Plant - MLE 25% Settled Sewage : 75% BTF
The above pilot plant results are based on grab samples
taken morning and afternoon. Frequent "reality" checks
were made of the on site test results by taking duplicate
samples and having spot-check analyses taken in the
Experience and knowledge gained during the pilot process
has proven that the MLE process is a robust activated
sludge configuration. The process design was aggressive
as defined by the low sludge age (SRT) of around 10
days and < 8 days in summer, whilst still producing
excellent results with low levels of ammonia leaving
the process. The process also produced excellent performance
with respect to the reduction in parameters such as
BOD and phosphorus concentrations. Modelling of the
process has produced functional design criteria for
which an interim plant could be based.
contents of this paper are based on recent work undertaken
at the Ballarat North Wastewater Treatment Plant. As
such the author would like to acknowledge the following
people in preparing this paper:
Central Highlands Water Wastewater Treatment Team inclusive,
Mr. Peter Zemek - Zemek Environmental Pty Ltd, and
Mr. Danny McLean - Process Operations Manager, Central
Zemek, P.M (2001), Short Term Improvements For The Ballarat
North Wastewater Treatment Plant - Status Report 1,
P.M (2002), Short Term Improvements For The Ballarat
North Wastewater Treatment Plant - Status Report 2,