FOCUS #4

Comparing Consequence Analysis- a Practical Method to Find the Right Solution for Wastewater Treatment

Email: peter.ridderstolpe@wrs.se
Info: http://www.swedenviro.com

1. Introduction

In Sweden, most of the wastewater treatment systems were built during a short period between 1970 and-1980. Generous subsidies from the state made it possible to construct thousands of treatment plants and ten thousands of kilometres of sewage pipes. This large investment allowed to connect approximately 90% of the population to central treatment systems, all with very uniform design.

Now after 25-30 years of operation a lot of pipes and plants require renovation.The question how the sewage treatment systems should be renewed has been subject to an intensive debate during the last decade. Two politically opposing camps are visible: those who are defending the Swedish line to construct large and central systems, and those who claim that a shift in systems must be done towards source separating systems and more simple nature based system. At the beginning of the 90s, confrontation was often hard and without nuances. Now the confrontation has developed more into a dialogue, partly due to the increase of knowledge of the people involved, but also because the political trend towards "ecological and sustainable development" made ecological thinking more appropriate.

Unfortunately, in spite of the political interest in ecological solutions, development and research of alternative wastewater treatment technologies has been neglected by the authorities. As a consequence, a gap has developed between the expectation in the new solutions and what is really known by practical and scientific experience.Some research has been carried out in order to illuminate the consequences of different sewage systems. The value of the results from these research projects is limited, due to the low level of development of different alternative technologies. Also, the research describes energy and resource aspects on a high level of generalisation, but doesn’t penetrate into the practical, economical and juridical aspects that often are the guiding criteria for the decision making in the concrete case.

For the a municipality with responsibility for wastewater planning, the lack of developed and proven technologies as well as the lack of simple tools for planning causes problems when different options for improvement or upgrading have to be evaluated. Habitual thinking and preconceived opinions may often obstruct a fruitful planning process. For ecological engineers, it's a challenge to help the decision makers out of the blind alley.

In my work as a consultant in wastewater management I have found, that locked positions can be opened and mind can be changed, if the decision makers can be lead to focus treatment results rather than different technologies. In this article I will briefly describe the method I use to help decision makers to find the right solution.

2. The planning method

1. The system boundaries must be defined, geographically as well as physically. For example:

• Which properties are, or should be, included?
• Should parts of the receiving waters (e.g., a wetland or a ditch) and/or agricultural land (e.g., for irrigation or use of sludge) be included in the treatment system?
• Does the system start at the boundary of each connected property, or could/should the plumbing in the houses be included? (Systems involving source separation require changes in the plumbing.)

2. The actors and their roles must be identified. For example:

• Municipality: could be the land owner and/or the local environmental and planning authority. The municipality could also be the owner of the system
• Property owners: are usually those who use and pay for the system with their fees
• Farmers: could be constructers who sell or lease land for the system, or receivers/users of nutrient resources from the system
• Contractors: operate the whole system

• What goals have been set for the receiving water in the local water planning document?
• What demands do other users have on the receiving water, e.g. for bathing, drinking water etc.?
• What possibilities exist for recirculation of nutrients from the system (i.e., does suitable agricultural land exist, are farmers interested in cooperating etc.)?

Answering these questions together with the client gives a framework for the planning process. The next step is to investigate and describe different system options. Each option should be investigated and described according to the framework, and a report should be made on how well the standards will be met. It is important to describe the options not only in economic terms but also in terms of performance and the other goals.The final step is to compare the alternatives and come to a decision. This step also involves, implicitly or explicitly, a weighing of the relative importance of the various goals.

3. The case of Vadsbro

After 30 years of operation it was concluded in Vadsbro, that the collecting system and the plant had to be renovated. To avoid peak-flows from storm water runoff and dilution of wastewater by ground water the municipality decided to renovate the collecting system but couldn’t decide how to renovate the old and obsolete treatment plant. During a long period of years the choice of technology for upgrading was discussed.

The people in charge in the administration suggested a modern package treatment plant, but among the politicians there was a will to find some more "ecological" technology for upgrading. Options like irrigation for agriculture purpose, treatment in constructed soil filter beds or wetlands were proposed, and some people even proposed a change of the whole system to a urine-separating system.

To find a solution the community asked for help from WRS AB. The consultants started planning work by making the decision makers discuss targets instead of technologies. Instead of discussing advantages or disadvantages of different technologies, the idea in that process was to let the decision makers get aware of the different possible goals of treatment, by discussing the need of environmental pollution control and public health protection, relative to economy, legislation and other practical aspects. Quite soon an agreement on targets was reached. The hygienic and the environmental demands, including recycling of nutrients were expressed. The "terms of requirements" included the desired functions of the system, but also expressed reasonable cost limits for investment and operation.

The next step in the planning process was to investigate different options for upgrading that possibly could achieve the "terms of requirement". From an investigation done by the consultant group, six alternative solutions were described. All the alternatives should be possible to accomplish. To get enough information to evaluate the practical and economical aspects of their implementation, it was necessary to pre-prospect all alternatives carefully.

All alternatives were then presented to the decision makers in a small report. The report made clear, that there can be widely varying technical means to achieve the same goal. This was a surprise for many of them. Presenting the alternatives with the help of principal sketches made it easy for them to understand how the different systems worked and what impact they would have on the landscape. Describing the consequences of each alternative in terms of the categories - agreed upon in the initial requirements - made the suggestions of the consultants easy to compare and evaluate.

After a short discussion the politicians could decide to choose the alternative called, "treatment with a biofilter ditch". This alternative was chosen because it was robust, flexible and inexpensive. Compared to the package treatment plant that had been one of the favoured alternatives before, the biofilter alternative was significantly less expensive and more efficient for both pollutant reduction and nutrient recycling.

4. Reading more on Vadsbro

The booklet gives examples of how the terms of requirements can be formulated and used in the planning process. It also evaluates a number of relevant wastewater technologies from the "point of the source" to the "end of the pipe", such as:

• Treatment in forest irrigation
• Treatment in stabilisation pond with calcium precipitation.
• Treatment in a biofilter ditch.
• Treatment with crop/wetland rotation
• Treatment in an open sand filter
• Treatment in a package treatment plant

The booklet can be ordered from WRS Uppsala AB, Sweden. The English version costs 20 USD (delivery cost not included). Mail to: peter.ridderstolpe@wrs.se. More infomation can be found on the homepage of Swedenviro. http://www.swedenviro.com