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In this part, we make a brief introduction of phosphorus and current water infrastructure in Sydney. Then we use material flux analysis (MFA) to track the inputs, stocks and outputs of phosphorus in Sydney region. As MFA results, we provide a conceptual infrastructure plan for a sustainable use of phosphorus in Sydney.
History about phosphorus
In 1669, phosphorus was first isolated from urine by Hennig Brand. Phosphorus is primarily found in inorganic phosphate rocks nowadays (Jefferson Labortatory, 2011). Phosphorus becomes a critical resource in fertilizer in today's agricultural.
Water infrastructure in Sydney
In the Sydney region, Sydney Water Corporation (SWC) runs 10 water filtration plants, and utilises 259 service reservoirs to supply of potable water to 4 million residents. 17 inland plants and 10 ocean plants are operated by SWC (Moore, 2011, SWC, 2002). On the other side, wastewater and stormwater are managed separately in Sydney.
Analysis of phosphorus in Sydney
In this section, the analysis of phosphorus in Sydney is based on the data of year 2000 (Figure 1, Moore, 2011). The Sydney region have a small part of agricultural but no major phosphorus related industry (Moore, 2011, ABS, 1998,2000). Most phosphorus related activities come from household sector and commercial and government sector (Moore, 2011).
4.1. Import of phosphorus in Sydney
According to Figure 1, the imports of phosphorus in Sydney are 5992 tonnes/year in four main categories, food production (2090 tonnes/year), animal feed (1545 tonnes/year), detergent (1244 tonnes/year), fertilizer (420 tonnes/year). And other phosphorus related productions contribute totally 693 tonnes a year.
Figure 1: Substance flow of phosphorus in Sydney, 2000 (tonnes)
Figure 2 shows the percentage of phosphorus imports in Sydney. To be more exact, food production for the largest proportion (35%), while animal feed and detergent make up 26% and 21% of the total phosphorus import. Fertilizer represents a less percentage only 7%.
Figure 2 Percentage of phosphorus import in Sydney
4.2. Export of phosphorus in Sydney
On the other hand, from Figure 1 only 2911 tonnes phosphorus, half of imported amount, was exported out of Sydney. The rest amount of phosphorus accumulates the stock of phosphorus in the Sydney region. The ocean outfall is consisted of 2664 tonnes (91.5%) of the exported phosphorus.
4.3. Stock of phosphorus in Sydney
In Figure 1, it describes that agricultural land, landfill and non-agricultural land have the highest phosphorus accumulation. Agricultural land, landfill and non-agricultural land account for around 35%, 27% and 16% of the total phosphorus accumulation respectively(Moore, 2011).
Conceptual design of infrastructure
As the result of analysis of phosphorus in Sydney, we can make improvements in all the parts of import, stock and export. Compared with current status, the new infrastructure system can provide Sydney a phosphorus recycling system. This system requires a less amount in phosphorus import and stock, which can lead to a significantly smaller phosphorus export in the future (Figure 3). In our plan an ideal Sydney infrastructure could contains these six parts in the future.
Figure 3 current status and ideal conditon of phosphorus in Sydney (tonnes)
5.1 Phosphorus recycling in household
The household sector in Sydney region consums phosphorus around 62% of the total amount imported out of the system (Moore, 2011). Beyond all doubt, a well-designed household phosphorus recycling system can play an important role in sustainable use of phosphorus.
5.1.1 Install "dry" toilet - urine separation system
It is common sense that human urine is a small part (1-1.5 litres per person a day) of the households wastewater but it contains the largest amounts of nutrients. Human urine is estimated to contain up to 70% of the phosphorous in human excreta (Drangert, 1998). A study conducted by Professor JÃÂ¶nsson shows urine contains approximately 70% of N (nitrogen) and 50% of P (phosphorus) and K (potassium) among ordinary Swedish household wastewater (JÃÂ¶nsson H, 2001). In agricultural and horticultural activities, urine has the equal fertilising effect to chemical fertiliser for phosphorous (JÃÂ¶nsson H, 2002).
Urine separation, commonly called "dry" toilet deals with the separation and consequent removal of human urine from the blackwater system. With the developing technology of urine separation. With academic research and public practice of urine separation in recent 10 years, the technique of "dry" toilet is ready for household, Therefore, household urine separation system is highly recommended in new Sydney infrastructure development. It is an cost-effective and environmental-friendly method to recycle phosphorus through urine separation in Sydney region. By the transformation of human urine in households to crop fertilizers in agriculture, urine separation can both decrease the phosphorus import in agriculture and reduce the burden of wastewater treatment plants.
5.1.2 Install greywater recycling system
Greywater makes up 50ââ‚¬"80% of wastewater in household, which typically comes from domestic activities such as dishwashing, laundry, and showering. We divide household greywater recycling project into two stages with two different types of household greywater recycling systems. In the first stage we recommend greywater diversion device which is a simple recycling system. While greywater purification is more complicated and could be taken into practice in a long term plan in second stage.
In stage 1, the simple greywater diversion device can distribute untreated water for toilet flushing or garden irrigation in household. Although this method can slightly reduce phosphorus amount in every single household, it helps to large decrease in a whole phosphorus flow of Sydney. Greywater diversion device is obviously a good practice without financial burden in households.
In stage 2, greywater purification enables treated greywater to be stored and used as potable (or near-potable) water. As a long term plan, this stage need more researches, surveys and a integrated feasibility study.
5.2 Phosphorus recycling in water plants
Eutrophication of the sea is a serious problem worldwide and the high level stock and export of phosphorus results in eutrophication problems in Sydney these years. According to Figure 1, in year 2000 in Sydney region 2664 tonnes (almost 90% of total amount) phosphorus export out of the system by sewage system and treatment plants. It is time to take action to decrease water emissions of phosphorus and nitrogen in Sydney, especially in those ocean plants operated by SWC.
Phosphorus in wastewater comprises two parts, soluble and particulate phosphorus. Particulate phosphorus can be removed from wastewater through traditional approaches such as chemical treatment, activated sludge treatment, or a combination of both (Yall, et al., 1976). The classic method cannot remove soluble phosphorus completely. But biological treatment is efficient to remove soluble phosphorus from wastewater. For instance, biological nutrient removal (BNR) is efficient to remove phosphorus and nitrogen from wastewater through the use of microorganisms (Metcalf, et al., 2003). However the cost of BNR is relatively high.
In today's industrial processes, enhanced biological phosphorus removal (EBPR) is quite popular because of its advantages both ecologically and financially. Polyphosphate accumulating organisms (PAOs) are designed to play an important role in EBPR process to remove phosphorus from wastewater (WEF and ASCE/EWRI, 2006). Moreover, after separation of bio-organisms from the treated water, these biosolids have a high value as fertilizer for agricultural plants .
For a better effect of phosphorus recycling through biological treatment, SWC hould increase the capital investment to upgrade existing ocean treatment plants or construct new plants. On the other side, SWC is responsible for building up new plants in Sydney's west, especially Parramatta region, as significant population growth in recent years.
5.3 Phosphorus recycling in agriculture
In Sydney agricultural activities only take less than 10% of the land. But it occupies almost 30% of the total phosphorus flow (Moore, 2011). Thus we need pay attention to this significant sector in the context of optimization of phosphorus use in Sydney.
A good practice of recycled water irrigation is taken place in parks, farms, race courses and golf courses in Sydney and the Illawarra. Every year about 4.6 billion litres of recycled water is used for irrigation in these places (SWC, 2010). This is not only a good water recycling system but also a proper phosphorus recycling system, which should be introduced to other new infrastructures state wide, even national wide.
Seasonal droughts always occur in Sydney and other cities in Australia. In this scenario, recycled water becomes a relatively reliable alternative water supply which can easily use on-site. After treating wastewater produces biosolids, which are rich in the nutrient (nitrogen and phosphorus) and can benefit composting and rehabilitation on agricultural lands. In addition, water recycling in agricultural sector helps to save precious portable water and large capital investments in infrastructure, such as installation and maintenance cost of long distance pipes for water supply and wastewater transportation.
The analysis results reveal that the status quo of phosphorus in Sydney region is not in a environmental friendly pattern. To set up a new infrastructure system is a fundamental step to use phosphorus sustainably. It is more essential and important to develop public awareness of phosphorus affection on the environment. Changing consumption pattern, such as using P-free detergent in daily life, which play a key part in lower import of phosphorus into Sydney and consequencely relieve the pressure of sewage system and treatment plants. In summary, the cooperation of public participation and technological developments can improve a sustainable use phosphorus in greater Sydney region.