Technology Selection and Design

During the first phase of a project, the starting point and baseline for the longevity of a wastewater treatment project is set. Accuracy andadequacy of the design to the local conditions is one of the key success factors for a sanitation system. To achieve this, data collection for project and site preparation and technology selection are building the basis for the actual design works. Moreover, this first project phase involves the initial time planning for the project from design up to commissioning.

Main considerations during these activities associated to the first phase can be summarised as follows:

Project Time Line Planning

Besides the time plan provided by a potential project employer, who approaches a designer for system design, the designer himself needs to have a clear time line for his activities and the activities associated to the construction phase. This timeline not only builds the basis for accurate budgeting, but it is also essential for cooperating with other parties involved.

To ensure the success of the project and to avoid any delay, it is very important to define a realistic time schedule, taking in account the several permissions to be collected, the bidding process (in case of public works) and the real time of executions by the company (also see Implementation).

For time planning, the following aspects need to be taken into account:

• Foresee “buffers” for potential delays during the design process: additional data collection needs, changes in project siting, administrative clearances/permissions.
• Foresee “buffers” for potential delays during construction process: delay in material purchase, administrational clearances/permissions, additional excavation works needed.
• Foresee time for system commissioning – it is a critical phase for assuring the quality of the construction works, as well as for preparing a smooth system-hand-over to the operators and owners of the systems and therefore has to be accurately budgeted for in the time planning.
• Take into account local circumstances like weather patterns (e.g.: monsoon seasons) and festivals (e.g.: holiday periods), which can take an influence on work progress.
• Take into account time for system stabilisation, where mentoring of the operating parties might be necessary via the system designers (or other experts familiar with the respective technology) might be necessary.

Data Collection

Baseline data are crucial for technology selection, siting of the treatment line and finally designing a system – but also for choosing the best management practice for operation and maintenance. Thus, prior to the selection of any wastewater treatment technology, a detailed examination of the self-sufficiency and technological capacity of the respective community is necessary.

Specifically, the following data should be collected:

• Wastewater quality and quantity in the course of a day (and seasonal variations, if available).
• Climate data involving a historical series of monthly minimum, maximum and average temperatures and monthly rainfall (for a period of at least 10 years); extreme rainfall data. Re-use potential (e.g.: fresh-water needs for irrigation or flushing purposes) including seasonal variations (e.g. based on water balance).
• National and local legal framework for effluent and re-use invalid link.
• Availability/reliability of power supply (power cuts, variations in voltage).
• Demographic development of the user community to estimate expected development in wastewater production.
• Geological, hydrogeological and geotechnical survey.
• Cadastral data (premises, plot boundaries and owners).
• Topographical profile.
• Mapping of existing networks: sewage, water supply, storm water sewage, electrical network, electrical connection points, other cableducts.
• Stakeholder analysis regarding financial and institutional capacities (including staff) for long-term system management.

Wastewater characterisation is the most critical activity in the data collection process. For characterisation, different approaches need to be used, depending on the type and source of the sewage. The collection of a good set of experimental data (sample analysis and flow measurements) are strongly recommended. The strategy of collection has to take into account the variability of the wastewater characteristics and it is important to provide both instantaneous samples at different time, rather than only 24h samples proportional to the flow. A survey on specific water consumption (of a family, or per guest in hosting structures) can also be useful. The experimental data should be comparable with literature data considering properly the specific context.

In case the data mentioned above are not available yet, the costs for preparatory studieshave to be included in the tender. Uncertainties in baseline data will lead to uncertainties in the design and finally to not well designed technologies/systems.

Technology Selection

The application of a single technological sanitation component is not sufficient to obtain the expected goals in terms of environmental and health protection; a sustainable sanitation system has to include all the components (physical parts and actions) required for the adequate management of human waste. The best combination of technologies to build up a complete sanitation system has to be selected for a specific site.

In urban and peri-urban areas, a successful sanitation approach is made more difficult by the complexity of the urban setting compared to the rural environment; sanitation issues demand an integrated developmental approach and are strictly related to urban planning, public health, stream restoration, flooding and hydraulic issues, agriculture, solid waste management, environmental protection, resources management, economics and politics, recovery and reconstruction strategies, religion and social aspects, etc. To understand the state of the sanitation system, see the Understand your system tool developed for the SSWM platform.

A feasibility study needs to be carried out and presented to stakeholders with the aim to select the preferred final solution for implementation. For agreeing on the selection criteria, it has to be noted that sustainable sanitation systems not only have to protect and promote human health by providing a clean environment and avoiding disease, but have to also be economically viable, socially acceptable, technically and institutionally appropriate, and protect the environment and natural resources. A good starting point to adapt the project development and the selection of the best management practices in different context is the SuSanA Thematic paper “Sustainable Sanitation for Cities” (PANESAR et al. 2010).

Thus, for the selection itself, not only the technical feasibility and economical parameters (investment and operation costs) should be taken into account, but also the effectiveness and the durability of the solution in the local context, the environmental impact and the social acceptance. A multi-criteria Life Cycle Analysis (LCA) analysis (REMY 2006) in many cases is a helpful tool in the preliminary phase of the design.

Summed up, the selection criteria should involve:

• Treatment performance (and robustness in case of systems expected to face severe variability in wastewater quality and quantity, unreliable operation and maintenance practices) – taking into account local/national effluent and re-use standards.
• Space requirements vs. availability and price of land (also to be considered for calculation of required capital investments).
• Rough estimation of expected capital investments, re-investments and operation costs (10 year life time) vs. local capacities and strategies for cost recovery.
• Requirements for skilling of management personnel vs. local availability and willingness of skilled personnel.
• Bottle-necks of system functionality (can the failure of single components lead to a prolonged stop of a whole system?) vs. local availability of technical competence and availability of spare parts.
• Geological conditions at the site to get information on the type of the soil to be excavated (presence of hard rock) and to define the foundation requirements (see also design).
• Hydrogeological analysis to define eventual interactions of the projected facility with groundwater.
• Local availability and quality of construction materials, consumables and spare parts.
• Local availability of Internet connectivity (for systems which are operated or monitored with a remote control).
• Dependency on a reliable power supply (respectively, take requirements for alternate power source, e.g.: generator, into account with regards to capital and operation and maintenance costs).
• Consideration of value chain, respectively, demand for products (re-use of wastewater, use of plants e.g. from Short Rotation Plantations).

Siting and Design

Dimensioning and siting of the systems should be carried out based on the analysis of the baseline data. The following aspects, tips and tricks, should be considered:

• After selection of the site, an expression of interest of relevant stakeholders can help to smoothen execution works and administrative organisation later on.
• Determine exact location of the system as early as possible to avoid multiplication of work for design adaptations and re-designing.
• Determination of the exact location should be based on the identification of the main constraints (e.g. underground networks, clearances of buildings, rivers, boreholes etc.).
• Avoid hard-rock underground wherever possible to keep excavation costs to a minimum.
• Avoid sites which would require cutting of trees wherever possible or budget for additional time needed for getting the cutting permissions.
• Use gravity flows wherever possible to reduce pumping requirements to a minimum.
• Integrate landscaping aspects into design process
• Stakeholder communication and involvement:
  • System owner’s needs and interests should be taken into account.
  • Questionnaires, deepen surveys and any other activities (e.g.: semi-structured interviews) oriented to involve the local communities are suggested to evaluate the possible impacts of social behaviours (i.e. waste disposal in sewer network, presence of animals, possibility of thefts), the social acceptance of the intervention and the real possibilities of a participatory monitoring evaluation).
  • Consideration of responsibilities for O&M management (e.g.: monitoring of O&M contracts) has to be included from the early design phase).

In this section, experiences made during system design and planning phase in context of the NaWaTech project are summarised. This involves both encountered challenges encountered and proposed solutions to overcome these problems in future projects. In the NaWaTech project, several administrative barriers were faced (e.g. change of responsible staff of implementation partners and thus non-signing of Memorandums of Understanding). These problems finally led to a change of several sites and a re-design of systems was required leading to an overall delay of the whole initial project phase.