A review of sanitation technologies for flood-prone areas

Despite the formal acknowledgment of sanitation as a fundamental human right, more than 600 million people still practice open defecation, most of them in poor countries. A part of this challenge is related to the type of natural environment such as floodable areas where flooding affects thousands of people every year and has a direct impact on their access to sanitation. Although there is a wide range of technological sanitation options for vulnerable communities, few publications explore their applicability to areas prone to constant natural floods, thereby hampering the possibilities for improving sanitation conditions in such areas. This review aims at compiling and consolidating current information on sanitation options for floodable areas with a focus on their technological, environmental, and managerial peculiarities. A systematic review identified 28 relevant publications presenting sanitation solutions for those environments. They were grouped into dry solutions and wet solutions. Our analysis showed that there is no single universal technology capable of solving the problem but instead, a set of different technological arrangements that could be implemented bearing in mind the environmental and social contexts in which they are inserted.


INTRODUCTION
A decade ago the United Nations organization acknowledged the right to sanitation as a basic human right for the full enjoyment of life (United Nations General Assembly ) and reaffirmed that it is the duty of the state to commit to the progressive implementation of that right by means of government efforts that include the implementation of the appropriate legal measures (United Nations General Assembly ). Small-scale or 'on-site' sanitation technologies can be considered the most suitable for rural environments with low population densities (Paterson et al. ), because they are simple, readily accessible, easier to design, and more liable to be socio-culturally acceptable (Mara ). In spite of all the solutions presented in the scientific and technical literature, a systematic approach to floodable areas and publications specifically focussing on them are comparatively scarce in the literature. There is a notable lack of more in-depth studies on this theme and of elements revealing the technological and management specificities that are necessary for sanitation in flood-prone areas. That dearth of information constitutes a knowledge gap and a challenge to be faced by communities living in such areas and by the institutions that are involved in sanitation.
These include, not only public institutions, whose functions include establishing public sanitation policies, but also research institutions and various non-governmental organizations (NGOs) that dedicate themselves to sanitation in floodable areas and also contribute to those policies.
This review aims to highlight the existence of that gap and contribute towards the production of systematic studies for flood-prone areas, compiling information on sanitation technology for these areas, with a special emphasis on the technological, environmental, and managerial peculiarities that make it possible to apply them in those environments.
The original incentive for the development of this paper was the need to obtain supporting information for the sanitation of floodable areas in the Amazon region, which covers a substantial percentage of the surface of the planet. However, the concepts and information obtained by this review may be also considered applicable to naturally flooded areas in other regions of the world.

Search method
For the purposes of this review, we considered scientific articles, review articles, and grey literature discussing or Key terms related to the theme of 'sanitation' were paired with key terms associated with floodable environments, searching the titles or abstracts for any of the following associations: ecosan OR latrine OR sanitation OR septic tank OR sewage OR toilet AND flood OR floodplain OR flood-prone OR monsoon OR varzea OR wetlands.
The pairing process resulted in 36 combinations.
In addition, in order to identify review papers that might

Study selection
The results of the database search were set out in an electronic spreadsheet and duplicated titles were then removed.
The remaining titles were evaluated independently.
At that stage of selection of the relevant titles, the criterion used was the presence at least one of the key terms in the title. Following that we proceeded to read the abstracts of the remaining publications to assess their relevance for the proposed objective of the review. The criterion used to evaluate the abstracts was the presence of information on sanitation technology for floodable areas or of a list of sanitation technologies. Those abstracts that failed to meet that criterion were removed from the list of studies.
Following that stage, we analyzed the texts of 66 publications to verify their contents and their compatibility with the study objective. As a result, some studies were discarded either because they lacked sufficient information on sanitation technology or because they were not relevant. By

FLOODABLE ENVIRONMENTS
Floodable areas such as coastal areas and estuaries, swamps and high groundwater areas, and areas prone to regular

APPLICABLE TECHNOLOGIES FOR SANITATION
Altogether we identified 21 sanitation technologies suitable for flooded areas (Table 2) and they could be grouped under the headings of 'Dry Solutions and Water Flush Solutions'. All of them are considered as being 'safely managed', as they are non-shared solutions and the excreta are, at least theoretically, disposed of in a safe manner (WHO/UNICEF ).
It must be stated that the solutions identified are not exactly technological innovations specifically for floodable areas, but instead, adaptations of consolidated solutions susceptible to being applied in such environments. Rainwater flood Similar to a flash flood, but less intense. Occurs in specific areas that are subject to heavy rainfall. Its impact is related to the impermeability of the soil. It leads to flooding of latrines in soil with poor drainage. Commonly occurs in floodplains.

Bangladesh Variable Variable Kazi ()
River flood Flooding associated with the seasonal rise in the level of the rivers. As it occurs in a known period of the year, it is relatively predictable. However, the great amplitude of the variation in the level makes toilet construction difficult as they need to be installed at extraordinary high levels.

Dry solutions
The solutions that come under this heading are usually lowcost set-ups, and their application is generally associated with low-income countries where the target populations are vulnerable (Mara & Evans ). The simplest toilet  may be required to obtain the best results. In the latter case, electricity supply must be available (Berger ).

Water flush solutions
The main feature of these solutions is that they require water to transport the excreta to some form of treatment unit by

NON-TECHNOLOGICAL ASPECTS -MANAGEMENT ISSUES
Technology per se is not sufficient to guarantee the success of a sanitation solution. It is considered that social aspects are essential and, if not adequately taken into account, failure of the implemented solution is likely to occur. This section covers some of these important elements.

Gender and sanitation
Gender inequality is a worldwide problem and present in all aspects of social life. The differences between men and women and their implications are mirrored in the access, management, and benefits brought by water supply, sanitation, and hygiene (Heller ).
In low-and middle-income countries, there are problems associated with difficulty in accessing water and sanitation as, for example, psychosocial stress (    adding to their discomfort, especially during menstruation (UNDP ).

Community participation
Those who will be users of

Social acceptability
Another important factor in determining the sustainability of a given technology is its acceptance by the local commu- All these mechanisms will depend on the lentic or lotic conditions that prevail in the water environment. In any case, there is a compromise in the quality and quantity of safe water to the population, increasing the risk of communicable diseases, such as waterborne and vector-borne disease (WMO ).
Among the main diseases related to floods are cholera, typhoid fever, leptospirosis, and Hepatitis A, as well as the

FINAL CONSIDERATIONS
During the analysis of the relevant publications, we observed that the main focus was on dry solutions in the ambit of ecological sanitation for the re-use of the subproducts in agriculture. Usually, those solutions were indicated for poor farming communities in developing countries like Brazil, Bangladesh, and Cambodia.
The available publications addressing the topics of sanitation and technology do not present sufficient technical information to enable an understanding of the specificities that would be necessary to implement them in the challenging environments addressed in this study. Even so, it identified 21 technologies that show technological potential for solving sanitation problems that exist for communities in flood-prone areas. Another aspect that the literature does not explore or provide information on is the role of the national or regional governments in the management of technologies which leaves a wide gap regarding the responsibilities of the actors involved in sanitation.
This survey has led us to believe that there is no single solution for sanitation in floodable areas in a universal technology perspective but instead, there are different technological arrangements whose implementation processes need to take into account the social and environmental contexts in which they are to be inserted.
Given that the proposed sanitation solutions are for vulnerable populations, it is imperative that there should be social participation in the planning and implementation processes. The desires, anxieties, opinions, and traditional knowledge of the beneficiary users must also be part of the process to ensure the success of sustained use. Solutions that require complicated maintenance (and that are associated with taboos, such as the need to handle feces) are not always acceptable by the communities.

Recommendations
Based on the survey made and the gaps identified, we recommend research be conducted and duly communicated on specific technological development frameworks for floodable areas, to gain an understanding of the technological performances of sanitation solutions in flooded environments. Also, further research on social approaches capable of interpreting user's appropriation of the solutions is necessary. We consider that institutions involved in sanitation must direct their efforts at the elaboration and dissemination of protocols with the complete information on the process of implementing sanitation technologies for floodable areas.

DATA AVAILABILITY STATEMENT
All relevant data are included in the paper or its Supplementary Information.