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SECTOR - Water/Sewerage COUNTRY - Norway

BACKGROUND
A residential area in the County of Akershus near Oslo has ca. 1200 inhabitants. There are severe problems with pollution from old onsite treatment plants contaminating the ground water used for water supply and the local watercourses. The local government has decided to investigate whether to

a) build a new conventional sewerage system with pipes leading to a central conventional waste water treatment plant (WWTP) or to
b) build and upgrade many small on site nature based waste water treatment plants.

In the conventional alternative the water supply will be centralised and come from the municipal water works in municipal water pipes. The sewage will be collected in a local network and pumped in a rather long conveyance pressure pipe to an already existing municipal WWTP. This pipe will also collect the sewage from several other areas in the northern part of the municipality of Frogn. In the nature-based alternative onsite sewerage treatment is localised on each house-owners plot. This is a combination of the following elements: infiltration of the black water to the ground, black water treatment in biological toilets, wetland constructions for grey water, wetland constructions for black water and grey water combined and open waterways or dams for storm runoff. The water supply will come from private wells using local aquifers. The amount of pipes will be reduced in this nature-based alternative. In the conventional alternative all operation and maintenance is taken care of by the municipality while in the nature based alternative the operation and maintenance must be handled by the residents themselves.

 

Figure 1. The nature-based alternative with onsite sewerage treatment.

INDICATORS
In this case the infrastructure evaluated is only the sewerage system itself included exchange of energy with the surroundings and the export of sludge. Water supply is not included in the analysis. Table 1 shows the score of each of the chosen indicators in the two alternative sewerage systems. Included in the calculation is the construction and operation phase. The manufacturing of pipes, pumps and onsite treatment plants are not included.

Indicators	Unit	Conventional alternative	Nature based alternative
Use of resources
Electricity	kWh/p·y	207,2	154,39
Use of water	m3/p·y	65,70	53,29
Fossil energy Construction phase (diesel) *	KWh/p	47,8	6,34
Energy recovery
Energy (hot water or electricity) from biogas	kWh/p·y	92,5	0
Less use of manufactured fertilisers	kWh/p·y	2,99	3,8
Phosphorus to agriculture	g/p·y	454,3	573,7
Discharge of phosphorus to recipients	g/p·y	40	70
Chemicals for WWTP	kg/p·y	22,3	0
Discharge to earth	g/p·y
Cd		0,038	0,013
Cu		7,44	2,48
Hg		0,022	0,0073
Pb		0,63	0,21
Discharge to air *	kg/p y
SO2		0,024	0,0032
CO		0,052	0,0069
CO2		12,8	1,7
NOx		0,22	0,03
Use of land	m2/p	0,3	3,0
Influence on the neighbourhood
Smell		very little	some
Noise		very little	some
Influence on the local habitat and landscape		some	some
Health and safety
Risk of infections of water from sewage		very little	some
Influence on recreation		very little	some
Inconveniences with operation and maintenance on the sewerage systems		very little	estimated to be 20 times worse than conv.
Annual cost incl. capital, maintenance, etc	ecu/p a	906 ECU /p year	649 ECU /p year

Table 1
*(Diesel for haulage of sludge and chemicals, and subsequent pollution are not included at present)

EVALUATION
Weighting of the indicators of the two alternatives and calculation of "penalty points" of the two systems are shown in table 2. The penalty point is calculated by multiplying the weight with the relative score.

A panel consisting of a sanitary engineer, an agricultural expert, a landscape architect and a person living in the actual residential area have evaluated the weight of each indicator. The weighting principle is based on each panel person's apprehension of the distance to critical level and the relative importance of the problem represented by the indicator. The indicators not transferred from table 1 to table 2 are either judged to be rather equal for the two alternatives or of little importance. Some of the indicators in table 2 incorporate several indicators from table 1 when they are having the same type of effect. This is to make the weighting process less complicated. The results of the weighting are shown in table 2. As shown the performance of each alternative is expressed relatively so that the highest value of an indicator is given the relative value of 100 and the other alternative a value relatively to 100.

Discharge of CO2 is given a relatively low weight because the relatively national contribution to global warming from the sewerage sector is very small (only 0,1 % according to Kärrman 2000.) Use of chemicals in the WWTP is also given a small weight because mainly iron sulphate is used which is no threat to the Oslofjord. The alternative with the lowest value for the penalty points is the most sustainable. Hence the conventional alternative has the best overall sustainability

		Performance of the systems (inverse)		Penalty points
Indicator	Weight	Conventional	Nature-based	Conventional	Nature- based
Net use of electricity	12	74	100	888	1200
Use of water	2	100	81	200	162
Fossil energy for construction (diesel) *	11	100	13	1100	143
Recirculated phosphorus	13	100	80	1300	1040
Discharge to water of phosphorus	11	57	100	627	1100
Chemicals for the W W T P	3	100	0	300	0
Discharge to the ground	8	100	33	800	264
Discharge to air. Local *	2	100	14	200	28
Discharge of CO2 . Global *	2	100	14	200	28
Use of area	12	10	100	120	1200
Influence on local area	6	95	100	570	600
Health and safety	8	90	100	720	800
Inconveniences with operation and maintenance on the sewerage systems	10	5	100	50	1000
SUM

Table 2. Weighting of the indicators of the two alternatives and calculation of "penalty points" of the two systems. * (Diesel for haulage of sludge and chemicals, and subsequent pollution are not included at the present)

It is very important to make sensitivity analyses on the weights to be able to find optimal and balanced distribution of the weights. One might find that only a small change in one of the weights may alter the conclusion, hence makes visible critical points to concentrate on in the weighting and score analysing process.

The trade off between cost and sustainability will normally be difficult but an important operation to make. This means that one will have to evaluate how much one will pay for sustainability. Looking at table 3 one sees that in this case one does have to make trade-offs between costs and sustainability because the conventional alternative is the most sustainable but the most costly.

Table 3. Comparison of costs and penalty points.

Parameter	Conventional	Nature based
Annual cost incl. capital, maintenance, etc	906 ECU /p year	649 ECU /p year
Penalty points	7075	7565

It is important to use the shown method with great care and not for instance draw the conclusion that the conventional alternative is ca. 7 % more sustainable than the nature based alternative because there is not any linearity between sustainability and the parameters in table 3.

If the water supply also had been included in the analyses together with the sewerage systems the analysis would have shown a more holistic picture, because water and sewerage are interconnected in many ways. Hence, setting the right borders for the systems analyses is very important.

TRANSFERABILITY
There is little transferability to other cases concerning whether conventional or nature-based systems are most sustainable because every situation and locality is unique and no generic conclusion can be found on what system is the most sustainable.

There is little transferability to other cases concerning the weights for local problem-indicators given in this example because these weights must reflect the local conditions. However one might consider the intentions behind the weights given to indicators reflecting global problems, when it comes to other sewerage systems.

The methods used in this case might be of interest to consider when performing sustainability analysis for other sewerage projects.

PROJECT CONTACT
Prof. Oddvar Georg Lindholm
Department of Agricultural Engineering.
University of Agriculture in Norway.
oddvar.lindholm@itf.nlh.no

Prof. Kine Halvorsen Thorèn
Department of Landscape Planning.
University of Agriculture in Norway.
kine.thoren@ilp.nlh.no

The answers in this matrix are based on the question "Is the nature based system more sustainable than the conventional system?"

Ecology	Answer	Economy	Answer	Social aspects	Answer
Are emissions to air, water and soil within the restrictions set locally and internationally? Are the emissions decreasing?	Water: OK decreasing Soil: OK, decreasing Air: OK, decreasing	Is the cost/ effectiveness/ and or cost/ benefits of the system reasonable compared to other systems? Compared to other needs in the city and to political goals?	Yes. The costs are lower.   Yes, also compared to other needs and goals.	Has the planning and decision-making for the infrasystem been done in a democratic and participative way?	Yes. Many public meetings. Discussions in the newspapers.
Is the use of natural resources reasonable compared to other comparable systems? Is the use decreasing? (eg fossil fuels, water, phosphorus, potassium)	Yes.   Water: decreasing Diesel: decreasing Phosphorus: decreasing	Are the citizens willing to pay for the services offered? Are the services affordable to all citizens?	Yes.     Yes	Is the function and the consequences of the system transparent to and accepted by the citizens? Is the system promoting responsible behaviour by the citizens?	Yes, but the citizens are divided in their views. Yes, but not all are motivated for the operation and maintenance.
Is the system allowing a reasonable bio-diversity with regard to the kind of area studied? Is the bio-diversity increasing?	Yes.   Increasing	Is the organisation(s) that finance maintain and operate the system effective?	The private owners will do that. The municipality would do this better however.	Is the system safe to use for the citizens? (hazards, health, well-being)	Yes, safe enough, but the conventional system is safer.
Is the system more or less sustainable than a conventional system regarding ecology?	More sustainable.	Is the system more or less sustainable than a conventional system regarding economy?	It is cheaper, but not more sustainable.	Is the system more or less sustainable than a conventional system regarding social aspects?	Less sustainable.

REFERENCES

• Jenssen, P. 1999. An overview of source separating solutions for wastewater and organic waste treatment. Managing the Wastewater Resource, 7-11. Jun.1999, Ås.
• Kärrman, E. 2000. Environmental Systems Analysis of Wastewater Management. Ph.D. theses. Chalmer University of Technology. Gothenburg.
• Tillmann, A.-M., Lundström, H., Svingby, M. 1996. Livscycelanalys av alternativa avloppssystem i Bergsjön och Hamburgsund. ECOGUIDE-projektet, Chalmers Tekniske Høgskole. Rapport 1996:1b. Göteborg, Sverige
• Wist, I. Sustainability Analysis of Sewerage Systems. 2000. M. Sc. theses. Dept. of Agricultural Engineering Agricultural University of Norway.