Publication (Technical report): The effect on sewage phosphorus loads of using phosphorus-free laundry detergent: Thurgoona case study

Publication Type:	Technical report / Consultancy
Publication Name:	The effect on sewage phosphorus loads of using phosphorus-free laundry detergent: Thurgoona case study

Reference Information

Ranson, G., Morgan, P., Cullen, P., Allen, D., Sinclair, D. and McGregor, D. (1998) The effect on sewage phosphorus loads of using phosphorus-free laundry detergent: Thurgoona case study. CRCFE Technical report November 1998, CRCFE, Canberra.

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ISBN:
858897407

Abstract:

Executive summary

In 1997, Albury City Council and the Cooperative Research Centre for Freshwater Ecology, with funding from The New South Wales Department of Land and Water Conservation, conducted a study into the contribution of laundry detergents to sewage phosphorus loads.

The study, conducted in three stages over six months, measured both the flow and phosphorus concentration of sewage from a catchment of around 350 households at Thurgoona near Albury, NSW. Baseline data was collected during the first phase of the study. The second phase of the study, the main study, measured the impact of phosphorus-free detergent usage while the third phase assessed long term changes in the community's use of phosphorus-free detergents.

The study resulted in an upper limit of 47% and a lower limit of 24% reduction in phosphorus in raw sewage when 64% of the community used phosphorus-free laundry detergent. This translates to a reduction of the existing load of 120 kg/day to around 65 to 90 kg/day for the total Albury community.
Reductions of this level would have a significant impact on phosphorus control at wastewater treatment plants. Potential savings of tens of thousands of dollars per year arising from a decrease in treatment costs could be expected, and the risk of increasing salinity and other pollutants resulting from the chemical removal of phosphorus would be significantly reduced.

The role of phosphorus
Phosphorus is an important constituent of all life. This nutrient occurs naturally in most plants and animals and readily enters the food supply of humans from these sources. Phosphorus also occurs naturally in most soils. Australian soils are generally poor in phosphorus, so it is added by way of fertilisers such as superphosphate. Thus most of our inland waters to contain some levels of phosphorus, either from natural sources or from those derived from human activity.

Excessive amounts of phosphorus may lead to the increased growth of algae and other microorganisms, causing water quality to degrade. Water containing large amounts of algae can become unsafe to drink. Ingestion of blue-green algae toxins can cause vomiting and diarrhoea, and may have longer-term effects such as liver damage and the promotion of tumour growth. Contact with algal blooms can cause skin irritation, thus impacting on the recreational use of water.

Several conditions are necessary for excessive algal growth:

The concentration of phosphorus reaches a critical level.
The normally more inert forms of phosphorus found in soils are augmented by more biologically active forms found in sewage effluent, including those from human waste and laundry detergents.
Parameters such as flow, turbidity, temperature and sunlight are at suitable levels for algal growth.

Good management of phosphorus requires that natural levels are not significantly exceeded. Naturally occurring phosphorus can be augmented from many sources. Non-point, or diffuse, sources include the run-off of agricultural phosphorous-based fertilisers.

Point sources such as sewage treatment plants are another source of non-naturally occurring phosphorus. Control of phosphorus levels using chemical removal processes is undertaken at sewage treatment works, to ensure that the amount discharged to the environment is within acceptable limits. It is important however to also initiate control at the origin, by stopping phosphorus from entering wastewater. A reduction in the amount of phosphorus reaching the treatment plant translates to lower running costs for the plant, while reducing the risk of increasing salinity and other pollutants resulting from the chemical removal of phosphorus. Source reduction also ensures that less phosphorus reaches the environment during periods of system overload or failure when untreated water is released. Much of the phosphorus in wastewater originates from human excreta and detergents which are discharged after usage into the sewerage system. Thus it is important to understand what urban activities contribute to phosphorus levels in wastewater, and their relative magnitudes.

Background to the Thurgoona study
The Albury City Council has long been at the forefront of authorities seeking to better manage their urban water resources. The PhosWatch campaign saw the phosphorus in influent sewage reduced from 142 kg/day to 112 kg/day as a result of an extensive education campaign aimed at changing the community's laundry and washing habits. A significant part of the PhosWatch campaign was the thrust to low and non-phosphorus laundry products.

The aims of the Albury-Wodonga-Corowa Phosphorus Action Campaign (PhosWatch) included:

To increase public awareness about the contribution phosphorus makes to increasing nutrient levels in our inland waters.
To provide the public with information about the sources of phosphorus in an urban context.
To provide information on what actions individuals can take to help minimise phosphorus in particular, and pollutants in general, at the source.
To quantify phosphorus reduction in sewage as a result of encouraging, at a local level, the use of zero/reduced phosphate detergents.
To provide valuable research data as part of the on-going program to improve water quality and to reduce the incidence of algal blooms in inland streams.
To act as a pilot for expansion of the program throughout NSW and nationally.
To provide input to the State Algal Management Strategy and to the Agriculture and Resource Management Council of Australia and New Zealand.

The Thurgoona Case Study follows a recognition that a follow-up campaign to the successful PhosWatch campaign was necessary. More information was needed on the contribution that laundry detergent makes to the phosphorus load, and what level and goals could be set if a campaign to use more non-phosphorus laundry products were to be initiated.

The Thurgoona Case Study
A sub-section of the Corry's Wood and St Hilaire estates of Thurgoona were chosen to participate in the study. The raw sewage flow and phosphorus concentration from the 356 occupied homes in the catchment were monitored during the three phases over six months in 1997.

The first phase, conducted during school term in March, was aimed at determining the community's normal usage pattern. The baseline data gathered during this period were acquired without any community announcement that a new project to study phosphorus had been initiated.

The second period, the main study period, measured the effect of using phosphorus-free laundry detergent on sewage phosphorus load. It commenced shortly after Easter with the announcement of the planned trial in the estates of St Hilaire and Corry's Wood. The announcement was followed by letter deliveries to households in the catchment, and with community meetings. A social survey, also conducted at this time, revealed that of the 385 houses in the study area, 356 were occupied. Of the occupied houses, 229 agreed to participate in the study and were given a free, eight week supply of non-phosphorus laundry detergent from a range of three products purchased by the Albury City Council. This allowed for a main sampling period of seven weeks running from April 22 through to June 10. The length of this period allows significant statistical averaging as well as providing an insight into the daily variations that exist within the normal weekly cycle. Like the baseline study, this study period did not include school holidays, although it ended with a public holiday, the Queen's Birthday. The average temperature during this main study declined by more than 10 degrees as the community moved from a warm autumn to early winter. A social survey, undertaken after the main study period ceased, gathered data on the effectiveness of the offered laundry detergent and other aspects of the trial.

The third and final period, the follow-up study, ran from August 2 to August 26, another period of continuous schooling. This part of the study was aimed at gauging the medium term success of modifying the community's laundry detergent usage habits. It was conducted some time after the last distribution of free, non-phosphorus laundry detergent, to ensure that any remaining supplies had been used. Chemical samples were collected for 21 days, however the flow record was interrupted by a recorder failure at day eight and difficulties in stabilising the record until day 12. Thus only limited data is available from this period.

Results
The results from the Thurgoona study are very promising, especially when viewed with the available social data. The overall reduction in phosphorus load during the period of phosphorus-free laundry detergent usage was 47%. This figure represents an upper limit on the amount of reduction, and is due to both changes in flow and changes in phosphorus concentration from the baseline to the main study period. The measured flow data for this study are inconclusive, which translates to uncertainties in the measured load to give a possible lower limit of reduction of 24%. This represents a load change due only to change in phosphorus concentration, and is therefore independent of changes in flow.

These results were obtained with a community participation rate of 64%, 25% of whom were already using phosphorus-free detergent. No attempt is made to adjust this result for the participation factor as there will always be members of the community who will prefer to use phosphorus detergents. For the study community, the reduction was from a baseline load of 2.5 kg/day to 1.3 kg/day. Assuming similar participation levels and a dominantly domestic source, it is anticipated that, on a city wide basis, the average daily load of phosphorus discharged to the treatment works could fall from the current level of 120 kg/day to around 65 kg/day, although in reality this latter figure would be elevated by some industry contribution.

The results also indicate that despite the availability of free laundry detergent and an increase of laundry activity due to its availability, the community also practiced water conservation which is part of the overall strategy. Indeed an in-depth study of flow into the Albury treatment works determined that over the last eight years, despite increases in population and industry, that there has been no net increase in flow. The practice of using full laundry loads is believed to be a significant contributor to this flow reduction, along with other waterwise practices.

A more detailed analysis of the reduction in phosphorus load shows that the decline is greater for the flow component, assuming a constant concentration, than it is for the load component assuming constant flow. Two major possible causes are:

Laundry activity is associated with a period of rapidly changing flow. The flow changes over a factor of 10 during the principal laundry period.
Errors in the individual depth readings, which are converted to flow, are proportionally greater than those in the phosphorus concentration determination.

The analysis of individual components and their interaction is able to place upper and lower limits on the results of the study. The lower limit for the reduction in phosphorus load is that component estimated to be due entirely due to changes in concentration. This was determined to be a 24% change. While not as significant as the overall value of 47% it still represents a significant change. If this level is applicable then the effect on the inflow into the treatment works would be to lower the current level of 120 kg/day to 90 kg/day.

Analysis of the follow-up study data shows a partial return to baseline community washing habits. Phosphorus load differs by only three percent between these two periods, however analysis shows that the proportion of components has changed. Flow increased by 15% from baseline levels while phosphorus concentration decreased by 10% (0.26 kg/day). The decrease in phosphorus concentration occurs mainly during the mid morning, the time of most laundry washing, indicating some acceptance and continued use of phosphorus-free laundry detergent following the main study period.

The future
This study highlights the contribution that laundry detergent phosphorus makes to the total load of phosphorus entering a sewage treatment plant. Environmental Protection Agency standards for the release of water from plants such as Albury require that the level of phosphorus be less than 0.3 milligram/litre on a 90 percentile basis. Other studies, notably the study undertaken by Melbourne Water at Whittlesea, suggest that biological nutrient plants, such as that operated by Albury City Council, operate more efficiently at lower level of influent phosphorus and thus may be able to reach Environment Protection Authority standards without the assistance of the current practice of chemical dosing.

Reductions or even elimination of chemical dosing may remove potential salinisation and mineral pollution problems as well as creating savings by reducing dosing agent costs. This evidence points to a need to review the operations of biological nutrient removal plants and the practice of chemically dosing the effluent.

It is therefore recommended that, should funding become available, a detailed study of the Albury City Council's wastewater treatment plant be carried out to determine:

The current levels of the influent phosphorus load and its variation.
The average residence time for particles participating in the biological process.
The tuning of the biological process for the optimal removal of phosphorus and other nutrients such as nitrogen.
The current levels of phosphorus and nitrogen before chemical dosing.
The current levels of phosphorus, nitrogen and unused dosing agent in the overall effluent.

Depending on the nature of the above results it is proposed to then seek community cooperation for a major trial, to determine the optimal characteristics of the plant under a reduced phosphorus load by repeating a significant portion of the above monitoring.

It is stressed that there are significant savings as well as significant environmental gains to be made if the current pointers to improved efficiency under reduced phosphorus load can be validated. The ability to cause and sustain these expected efficiencies is strongly linked with the level of phosphorus in laundry detergent and the ability to influence and change the laundry detergent preferences and habits of the community.

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