Clean energy water disinfection for small, remote and rural communities

Design team members: Kishore Chittella, Sapandeep Matharoo, Naveed Rahman

Supervisors: Dr. John S. Zelek

Background

It is well known that in many parts of the world access to clean water in a cost effective manner is difficult. This is particularly emphasized when disaster strikes and small communities are faced with disinfecting their water supply for drinking purposes. Rural and remote communities also face this challenge on a daily basis due to infrastructure constraints like lack of reliable supply of electricity. It is desired to have a water disinfection system powered by a renewable source of energy so that irrespective of the availability of electricity, communities will be able to access clean drinking water and also assist in the reduction of carbon footprint.

 

Person drinking dirty water

[1]

Access to clean water in rural and remote communities is of growing concern due to the increase in population and the dramatic decrease in the world’s fresh water supply.  Many existing products/designs are available to provide these communities with disinfection mechanisms capable of providing self-sustainable clean water.  As part of the design process of the proposed project, thorough research is performed on existing products to determine their shortcomings as a viable candidate for the constraints imposed by the contest, and to serve as informative prior art to provide a better understanding of how to improve the design process, and to provide a better understanding of how to design a unique product to meet the imposed requirements that do not currently exist.

Project description

The motivation for the project topic arises from our interest to participate in the WERC Environmental Design Contest which is held annually at the New Mexico State University and aims to bring student teams to design solutions for real-world problems. The design consists of two components: a water disinfecting methodology and an energy harvesting mechanism. Our design team consists of two groups each from Systems Design Engineering and Environmental Engineering. The Systems Design Engineering team will focus on the design of an energy harvesting mechanism for the water disinfection system.

The problem area that has been identified is the lack of usage of renewable sources of energy to effectively disinfect water. A water filtration device that harvests non-fossil source of energy to effectively disinfect water according to the World Health Organization drinking water standards for bacterial contamination would be highly desirable in rural communities and areas with little or no access to fossil energy. Several filters and water disinfecting systems exist but none are powered by renewable energy sources. As indicated in the guidelines of the competition, the goal is to develop a standalone, non-fossil based energy source for a water disinfection/treatment system to provide 3000 gallons per day of clean, disinfected water to be used for small, remote community.

Design methodology

Based on research and analysis conducted by the Environmental Engineers, there are four aspects of the problem that define the scope of this project:

  • A mechanism to introduce infected and remove disinfected water from the system with a capacity to handle 3000 gallons per day
  • A system to harvest renewable energy resources, store energy efficiently and utilize it to power the UV disinfection mechanism
  • A method to optimize energy consumption to improve energy efficiency
  • A system to store or distribute clean water

Furthermore, as part of the rules and constraints determined in the task provided by New Mexico State University [2], a major objective of this proposed project is to meet the outlined design considerations and the evaluation criteria.  The following criteria relevant to the energy harvesting portion of the project are presented in the task provided:

  • Easy to implement, maintain and operate throughout the year
  • Portability
  • Cost effective
  • Applicable to rural and third world environments
  • Reliability
  • Energy efficiency
  • Daily throughput of 3000 gallons per day

The following functional analysis diagram illustrates the various components and interactions of the system:

Functional analysis diagram indicating components and interactions of the system

Four non-fossil fuel energy sources were examined to determine the best candidate to supply power for the disinfection system based on size, portability, cost, complexity and ease of implementation. The candidates include: geothermal heat pump, wind turbine, solar power, and human kinetic energy. As a result of the constraints, the geothermal, wind and solar energy sources were eliminated. With human kinetic energy as the chosen medium for the energy, the physical concept of the device can be visualized using the functional analysis diagram provided.

The kinetic energy source in the form of either a hand crank connected to a permanent magnet DC motor or a bicycle connected to a generator will provide the necessary power to operate the flow pump, UV lamps, as well as the integrated battery to store excess charge from which the flow pump and UV lamps can be powered when a kinetic energy source is not present.   Various battery implementations were considered including a nickel-metal hydride battery, nickel-cadmium, lithium-ion battery, and a lead-acid battery, however ultimately the lead-acid battery was chosen.  This is due to the fact that nickel-cadmium batteries possess heavy memory effects in which the battery needs to be fully discharged to maintain battery longevity and would hamper the continuous operation of the product, and lithium-ion batteries are not very cost effective for high powered applications [14].  Nickel-metal hydride batteries are a very common source of rechargeable batteries, however their voltage ratings are much too low to run a high powered application such as a pump.  Theoretically, the voltage could be increased by adding more nickel-metal hydride cells in series, however this would greatly increase the cost of the solution, therefore lead-acid batteries provide the best alternative for cost effectiveness.  Lastly, for removal of turbidity and sedimentation, a combination of steel mesh filtration and cartridge/membrane filtration would be added into the system to compliment the flow of water as an added disinfection mechanism.  A figure showing the system and its high level components is shown below.

A diagram illustrating the relationships between high-level components of the system

Figure 2: Proposed concept diagram

Work on the modeling front involves calculating the energy and power requirements, UV dosage and intensity, exposure time and pump capacities. An integrated mathematical model will be developed to investigate the impact of modifying different variables on the design (sensitivity analysis). Furthermore, specific operational requirements and quantitative benchmarks will be developed through joint design sessions with the Environmental Engineers. Also, energy optimizations will be made to the final solution through regulating flow rate and UV lamp intensity based on system usage. Using a programmable microprocessor as an on-board embedded processor with analog-to-digital sensors to analyze and measure the input and output power of the proposed solution, energy optimization algorithms will be put into place to improve the efficiency of the system.

References

[1] Daily dos, October 15, 2010 <http://www.holamun2.com/news/daily-dos-big-gulp>

[2] New Mexico State University, October 15, 2010 <http://www.ieenmsu.com/programs/international-environmental-design-contest-at-nmsu>