PERIODO 2000 AL 2010: LIBERALISMO Y CON PLAN

In figure 1 an overview of different possibilities for handling of household wastewater and solid waste is given. The rectangles represent different types of waste, wastewater and treated material. The circles represent processes for treating the waste and wastewater. The darkly shaded frames indicate that water is added to waste or wastewater while the medium shaded frames indicate that no water is added. The lightly shaded frames indicate that the waste is inorganic. Each handling method has different costs and cleaning effects. The figure shows how complex the treatment process is with many possibilities for handling of wastewater and waste. Handling does not only include technologies for treating wastewater, but also changes in production processes or in consumption. The wastewater handling system therefore

includes the collection, transport, treatment, and spreading system. In some cases it may be advantageous to handle wastewater sludge together with food waste. Use of wastewater systems like source-separated systems instead of municipal sewage systems, can change the costs and handling possibilities for the waste-handling sector and in some cases, the demand for drinking water. Hence the saved or increased costs from these other sectors can be included to produce a comparison of the wastewater handling systems. Benefits such as the income from sale of «treated wastewater» as a source of macronutrients for agriculture can be included as a profit, see also Refsgaard and Etnier (1998). The standard calculations of

wastewater treatment costs from Statistics Norway (Hass 1997), for example, only include the costs arising after the wastewater has left the house. While this works very well when

inadequate when cost comparisons include decentralised systems, many of which call for special toilets or tanks to be installed by the house-owner. The whole chain for wastewater treatment is therefore termed «wastewater handling» to separate it from subsystems like cleaning.

Figure 1: Different possibilities for the handling of household wastewater and waste

Below, the different wastewater types and the treatment technologies used in the handling systems in this paper are described.

2.1. The wastewater types

Wastewater is often a mix of blackwater from ordinary toilets, using 5-10 l water per flush, and greywater. The mixed wastewater is collected in a septic tank for further treatment or sent through a common pipeline system to a sewage plant. Source-separation of the wastewater in blackwater and greywater is a potential future option. The blackwater is collected in a closed tank after use of a vacuum toilet system adding 1 l water per flush or after use of a waterless

Food Unsorted garbage to landfill Food waste Fodder Fertilizer/soil conditioner Disposable goods and packaging Non-food waste Reuse or recycling Waste to landfill or incinerator Water

Mixed wastewater Graywater

Faeces Blackwater

Toilet waste

Septic tank Storage

tank Liquid composting reactor Centralized composting or digestion Collection Composting at home Grinder/ shredder Storage tank Composting toilet Source separation Ecologically engineered system Sludge stabilization hygenisation Sludge to landfill

or incinerator Water to recipient

Irrigation water

WASTE-

WATER

WASTESOLID

1 , 2 or 3 treatment

o o o

toilet adding 0.04 l water per flush (Skjelhaugen (1999). The greywater is sent through a septic tank for further treatment afterwards. Based on this, the wastewater is classified in the following types according to the concentration of different matter in the wastewater and on the toilet technology:

· Mixed wastewater based on ordinary toilets, including greywater and toilet waste

· Toilet waste in the form of blackwater based on vacuum toilets

· Toilet waste in the form of blackwater based on waterless toilets

· Greywater

2.2. The treatment systems

The treatment systems studied are ecologically engineered systems including infiltration plants and constructed wetlands, liquid composting reactor systems and conventional 1*, 2* or 3* treatment systems including package treatment plants and centralised sewage systems.

2.2.1. The infiltration plants

The infiltration facilities evaluated are modelled according to the design guidelines by the Norwegian Centre for Soil and Agricultural Research (Køhler 1997) and the Norwegian Pollution Control Authority (Ministry of Environment 1992). An infiltration plant consists of a septic tank to keep the sludge and an infiltration unit where suspended and dissolved matter is removed. The treatment is based on infiltration of the mixed wastewater or the greywater through the soil. The cleaning processes mainly occur on the surface of the particles, where especially phosphorus is bound. Nitrogen and organic matter are based on cyclic processes. By the projecting design of the plants the choice of concept, design, material and

dimensioning must be adapted to the natural conditions. The infiltration plants can therefore be based on either local or added masses and with open or closed ditches. In Norway closed ditches are most common. The following infiltration plants are included in this model:

· Infiltration in soil

· Sand filter

2.2.2. Constructed wetlands

The constructed wetlands evaluated are modelled on facilities built and tested in Norway by the Norwegian Centre for Soil and Agricultural Research (Mæhlum et al. 1995, Mæhlum 1998, Køhler 1997). Constructed wetlands are typically installed for mixed wastewater or greywater treatment at a site where a wetland did not previously exist. The constructed wetland consists of a septic tank, a pump for intermittent loading of the vertical flow bed, a bed with vertical flow through coarse sand and/or lightweight aggregates, a planted bed with horizontal flow through sand and/or lightweight aggregates and an access port. The bed with vertical flow is an aerobic pre-treatment to enhance nitrification and reduce the biological oxygen demand (BOD) load. The lightweight aggregates can be used to improve phosphorus removal. Therefore different types of wetlands can be constructed according to filter material, vegetation, design and throughput. The types included in this paper are:

· Constructed wetland with sand

· Constructed wetlands with lightweight aggregates 2.2.3. Package treatment plants

In a package treatment plant the wastewater flows to an interception tank with three chambers. The first chamber serves as primary treatment, i.e. sedimentation. The second chamber is a pumping station and evens out variations in the flow. From there the water is pumped to a reactor, where it goes through aeration and biological and chemical precipitation or more simple treatment, depending on the type of plant. For more information, see

Refsgaard et al. (1998). In this study the biological/chemical package treatment plant implying 3* treatment is included.

2.2.4. Liquid composting reactor

In systems with source-separation of the wastewater in blackwater and greywater, the blackwater or eventually the septic sludge can be treated in an aerobic liquid composting reactor (Skjelhaugen 1999). Through liquid composting, the material is both stabilised and hygienised according to legal requirements. The greywater can be treated in infiltration plants or constructed wetlands described above. The blackwater treatment is not on site, but is often situated on a farm where there is a potential for recycling if the water content is relatively low, as is the case in blackwater. Thus, a higher number of households can contribute with

high concentrated blackwater and waste, thereby leaving a higher income potential for the farmer than when the content of water is higher, e.g. in wastewater. The cost-efficiency of these systems depends thereby on the material’s nutrient contents and the transport distances. Normally, organic matter with a high energy content has to be added to speed up the process. This can also be a proper treatment option for organic waste where costs and resources can be saved using a combined treatment with blackwater.

2.2.5. Centralised sewage plants

One option frequently proposed and used for wastewater treatment in rural Norway is to extend the sewage network to incorporate more houses. In a sewage network wastewater from many households, industry and public institutions are transported with common pipelines to centralised sewage plants. Several types of treatment processes are used with different combinations of mechanical, chemical and biological processes and depend on local conditions like type and condition of the recipients. Average figures from Norwegian municipal sewage plants for cleaning effect are used and described in Refsgaard and Etnier (1998) and Statistics Norway (1999a).

3. A model for optimal solution (as to cost-efficiency) at municipality