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Conference Papers | 1998 Conference Papers OPERATIONAL
EXPERIENCE IN TREATING TEXTILE WASTES DISCHARGING INTO
THE FARLEY WWTP
Michael Boake Process
Engineer,
Strategic Operations, Hunter Water Corporation
Derek Orrin Operator,
Farley WWTW, Operations Group, Hunter Water Corporation
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ABSTRACT
The
Hunter Water Corporation provides water and sewerage
services to approximately 420,000 people in the Newcastle
area (which is 2 hours drive north of Sydney). The Corporation
operates twenty-one (21) wastewater treatment works
(WWTW) which treat sewage from residential, commercial
and industrial customers. These works range in size
from small local plants treating sewage from a few hundred
households to large automatic plants capable of processing
sewage for over 200,00 people.
One
of the Corporation's works is Farley WWTW which receives
high pH waste from a large textile company in the sewer
catchment. Over the past fifteen (15) years this discharge
waste has caused a number of process problems which
have been minimised through actions taken by the operational
staff at the treatment works. This paper describes the
problems that have occurred at the plant, the effects
on the process and action taken to maintain good effluent
quality.
KEY
WORDS
Textile
Wastes, Tradewastes, Wastewater Treatment
1.0
INTRODUCTION
The
Hunter Water Corporation provides water and sewerage
services to approximately 420,000 people in the Newcastle
area (which is 2 hours drive north of Sydney). The Corporation
operates twenty-one (21) wastewater treatment works
(WWTW) which treat sewage from residential, commercial
and industrial customers. These works range in size
from small local plants treating sewage from a few hundred
households to large automatic plants capable of processing
sewage for over 200,00 people.
One
of the Corporation's works is Farley WWTW which receives
high pH waste from a large textile company in the sewer
catchment. Over the past fifteen (15) years this discharge
waste has caused a number of process problems which
have been minimised through actions taken by the operational
staff at the treatment works. This paper describes the
problems that have occurred at the plant, the effects
on the process and action taken to maintain good effluent
quality.
1.1
Farley Wastewater Treatment Works
Farley
WWTW is located 4km south east of Maitland. The Farley
Works services parts of Maitland, Telarah, Rutherford,
Aberglassyn and Gilleston Heights as well as receives
septic effluent and commercial wastes via road tankers
from neighbouring areas. Approximately 60% of the loading
on the Farley WWTW comes from a local textile factory
in the sewer catchment which discharges high pH waste
under a trade waste permit.
The Farley WWTW consisting of a Extended Aeration Activated
Sludge Process (Carousel) was commissioned in 1983 with
a design capacity of 50,000 EP (equivalent persons).
The
process units and schematic layout are described in
detail in the attachments to this paper. The current
loading on the plant is 35,700 EP (7.2 ML/day) and produces
a high quality effluent (typically BOD, NFR and total
Nitrogen less than 10mg/L) when not effected by high
strength trade wastes. Also a large part of the treated
effluent is being used for irrigation by local farmers
and washdown activities at the treatment plant.
Chemical
phosphorus removal with alum was implemented in 1997
in a Pollution Reduction Program (PRP) with the NSW
EPA. The plant is monitored by a SCADA (Supervisory
Control and Data Acquisition) System that represents
graphically the plant and equipment items, and warns
staff with alarms in case of process failures or disruptions.
The
local textile factory has an agreement with Hunter Water
to discharge waste which does not exceed a maximum flow
of 4.3 ML/day and an instantaneous rate of 61L/S. If
the pH exceeds a maximum of 12, a valve at the textiles
factory automatically stops the trade waste discharge
until pH is returned to a level below 12.
1.2 Textile
Factory Discharge Waste
The local textile factory which employs approximately
400 staff, has a number of processes associated with
the production of textiles. These processes include
weaving of fabric, preparation of fabric (scouring and
bleaching), dying and finishing.
Some
of the fabric is made on-site which involves sizing
of the fabric (which adds Poly Vinyl Alcohol (PVA) or
starches to strengthen the fibres), weaving and subsequent
washing. The majority of the fabric used on-site is
now imported and has unknown preparation in terms of
the chemical used in sizing. This imported material
is washed which may release unknown chemicals into the
wash water.
The
next stage of treatment is preparation of the fabric
for dying and involves scouring and bleaching of the
cloth. This process utilises a large proportion of the
caustic (80%) used on-site. The total daily consumption
of caustic on-site is of the order of 4.5 tonnes. The
bleaching process also utilises hydrogen peroxide. A
caustic recovery unit collects the waste stream from
the scouring process and concentrates it allowing it
to be reused.The caustic from the bleaching process
however does not go through the caustic recovery unit
and this is the main source of caustic in the waste
stream.
The
fabric is then dyed using a number of different processes,
both batch and continuous. The chemicals used in dying
are salt, small quantities of caustic soda ash and dyes
themselves. After dying the material is then finished
using resins and starches. Table 1 quantifies the characteristics
of the textile waste stream.
Table
1: Chemical
Characteristics of Textile Wastes
2.0 DISCUSSION
The waste stream from the textile factory has had a
number of detrimental impacts on the treatment process
at Farley WWTW. These have included :-
-
High oxygen consumption
- Predominance
of filamentous bacteria in the activated sludge process
resulting in sludge bulking and a reduction in the
available capacity of the sludge lagoons.
- The
potential risk of a total kill of activated sludge
biomass due to high pH (as occurred in June 1990).
Table
2 lists the history of problems that have occurred at
Farley WWTW due to the receivable of high pH waste from
the textile factory.
Table
2: List Of Effects Of Waste
From Textile Factory On Farley WWTP
| DATE |
INCIDENT |
EFFECT
ON FARLEY WWTW |
ACTION
TAKEN BY OPERATIONAL STAFF |
| 10
July 1990 |
Accidental
Discharge of 25,000 litres of 50% Caustic Soda discharged
to Sewer |
Incoming
effluent of pH 13.5 destroyed biological activity
at Farley WWTW |
- Increased
aeration of plant.
-
pH correction of biological reaction using acid.
-
Tankering of seed. Activated Sludge from nearby
WWTWs.
-
Aeration of maturation pond to treat effluent
while process was being established.
-
Shutting down discharge line from textile factory
while process was being re-established.
-
Increased pH monitoring.
|
| 1
November 1990 |
Large
Volumes of High pH wastes from textile factory |
- pH
alarm in Biological reactor recorded 9.5.
-
Poor settling in clarifiers and floc carryover
to maturation ponds.
-
Reduced biological activity in reactor.
|
Plant
Operation changed to bypass high pH incoming wastes
through sludge lagoons to reduce pH. |
| 29
August 1991 |
Operational
Problems with Caustic Recovery Unit |
High
pH alarm in Biological Reactor |
Plant
Operation changed to bypass incoming wastes through
sludge lagoons. |
| 16
March 1993 |
Faulty
pH probe at textiles factory resulted in textile
factory correcting wastes with acid. |
No
effect |
Assisted
textile factory staff in calibrating pH meter. |
| 30
July 1993 |
High
pH wastes from textile factory >12 |
-
High aeration required at PlantW.
-
Poor settling sludge.
-
Carry over of bulking sludge to Maturation Ponds.
|
Increased
aeration in Biological Reactor. |
| 26
November 1994 |
Suspected
High pH wastes from textile factory >12. |
Inflow
pH monitor at Farley WWTW was reading high |
Re-calibration
of pH probe at Farley WWTW. |
|
11 April 1996 |
Textile
factory carry out trial using CO2 Gas to reduce
pH in waste stream. |
Carryover
of sludge from clarifiers due to excess CO2 release.
|
CO2
gas trial was discontinued. |
16
May 1996
22 May 1996 |
High
pH 12.8 in waste stream |
-
Foaming in clarities and settleability problems.
-
Carryover of sludge into maturation ponds.
-
pH of 9.3 in effluent from clarifiers.
|
Plant
Operation changed to bypass incoming flow through
sludge lagoons |
16
October 1996
25 November 1996 |
Large
volumes of High strength wastes |
- Sludge
build up in clarifiers
- High
pH in Biological reactor
|
- Plant
operation changed to bypass.
-
Textiles factory taken off-line.
|
13
January 1997
17 January 1997 |
High
pH and flow after Christmas shutdown for 2.5 weeks |
- Sludge
build up in clarifier
-
High pH in Biological reactor.
|
Textile
factory acid dosed to reduce the effects on Farley
WWTW. |
7
April 1998
10 April 1998 |
High
pH and flow after Easter shutdown |
- Sludge
build up in clarifier
-
High pH in Biological reactor.
|
Textile
factory acid dosed to reduce the effects on Farley
WWTW. |
| 22
May 1997 |
High
pH and flow due to caustic recovery system |
- Sludge
build up in clarifier
-
High pH in Biological reactor.
|
Textile
factory acid dosed to reduce the effects on Farley
WWTW. |
| 22
January 1998 |
New
CO2 gas trial |
Problems
repeated as previously in April 1996 |
CO2
Gas trial discontinued. |
| May
1998 |
Waste
stream normal pH <11.8 |
Acid
dosing trial at Farley WWTW to control high pH wastes
in Biological reactor as well as assist chemical
P removal by reducing alkalinity in effluent. |
By
decreasing pH in biological reactor down to 7.5.
Activated Sludge Process performed excellently,
however Chemical P removal did not improve consistently.
|
3.0
CONCLUSION
Over the fifteen (15) years that the textile factory
has been operating and discharging high pH wastes (ie.
>11.0) to Farley WWTW, consistent problems have occurred
with :-
-
High Oxygen Consumption
- Sludge
Bulking
- Carryover
of sludge into Maturation Ponds
- Decreasing
capacity of Sludge Lagoons
- Potential
Risk of Biomass Kill.
Operational
staff action to combat these problems have involved
:-
- Increasing
aeration
- Increasing
sludge wasting
- Bypassing
raw sewage via sludge lagoons
- Installing
pH probes in Biological reactor as early warning
- Installing
pH probe in waste stream at textile factory with action
to shut off discharge valve when pH is >12.0.
- Carrying
out acid dosing trial at Farley WWTW (using sulphuric
acid to dosed biological reactor).
However, despite all these actions carried out by operational
staff which have assisted enormously in reducing the
frequency of the final effluent being outside the EPA
licence requirements, the potential of a major problem
still exists.
The
final solution to the above problem rests with the source
namely the textile factory who needs to carry out a
waste minimisation audit and install a pre-treatment
process that will reduce the pH in the tradewaste discharge
to < 11.0. As well as construct an on-site storage dam
(to hold one day's storage) in order to balance out
peak flows and tradewaste effluent quality discharged
to Farley WWTW.
Figure
1 - Farley WWTP Process Flow Sheet
Figure
2 Fact Sheet - Farley Wastewater Treatment Plant
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