Low concentration of zeolite to enhance microalgal growth and ammonium removal efficiency in a membrane photobioreactor

The aim of this work was to study the growth and nutrient removal efficiency of a mixed microalgal culture with and without the addition of low concentrations (0.5, 1, and 5 g L^-1 of total liquid volume in the reactor) of natural zeolite. A control test in which only zeolite was added into a similar membrane photobioreactor was also conducted. The addition of 0.5 g L^-1 zeolite to a continuously-fed membrane photobioreactor increased the microalgal biomass concentration from 0.50 to 0.90-1.17 g particulate organic carbon per L while the average ammonium removal efficiency increased from 14% to 30%. Upon microscopic inspection, microalgal cells were observed growing on the surface of zeolite particles, which indicates that zeolite can support attached microalgal growth. With higher zeolite doses (1 and 5 g L^-1) inside the reactor, however, the breaking apart of added zeolite particles into finer particles dramatically increased solution turbidity, which likely was not beneficial for microalgal growth and ammonium removal due to reduced light penetration. This work shows that low doses of zeolite can be used as microcarriers to enhance microalgal biomass concentration and ammonium removal efficiency, while minimizing zeolite dose would likely reduce the turbidity effects.

Regenerative water purification for space applications: Needs, challenges, and technologies towards 'closing the loop'

Human missions to establish surface habitats on the Moon and Mars are planned in the coming decades. Extraplanetary surface habitat life support systems (LSS) will require new capabilities to withstand anticipated unique, harsh conditions. In order to provide safe, habitable environments for the crew, water purification systems that are robust and reliable must be in place. These water purification systems will be required to treat all sources of water in order to achieve the necessary levels of recovery needed to sustain life over the long-duration missions. Current water recovery and purification systems aboard the International Space Station (ISS) are only partially closed, requiring external inputs and resupply. Furthermore, organic wastes, such as fecal and food wastes, are currently discarded and not recycled. For long-duration missions and habitats, this is not a viable approach. The inability to recycle organic wastes represents a lost opportunity to recover critical elements (e.g., C, H, O, N, P) for subsequent food production, water purification, and atmospheric regeneration. On Earth, a variety of technologies are available to meet terrestrial wastewater treatment needs; however, these systems are rarely completely closed-loop, due to lack of economic drivers, legacy infrastructure, and the (perceived) abundance of resources on Earth. Extraplanetary LSS provides a game-changing opportunity to incentivize the development of completely closed-loop systems. Candidate technologies may be biological, physical, or chemical, with associated advantages and disadvantages. This paper presents a survey of potential technologies, along with their inputs, outputs and requirements, which may be suitable for next-generation regenerative water purification in space. With this information, particular technologies can be down-selected for subsystem integration testing and optimization. In order for future space colonies to have closed-loop systems which minimize consumable inputs and maximize recovery, strategic implementation of a variety of complementary subsystems is needed.

Feasibility of anaerobic membrane bioreactors (AnMBR) for onsite sanitation and resource recovery (nutrients, energy and water) in urban slums

Slums are challenging locations for sanitation technologies. High population densities, a lack of water and electricity infrastructure, and space constraints combine to ensure that many traditional waste treatment technologies fail when implemented in this context. This paper proposes the use of anaerobic membrane bioreactors (AnMBRs) for slum sanitation. AnMBRs allow for localized water reuse, high quality treatment, and energy production at the point of treatment. A water, energy, nutrient, and mass balance was conducted on a theoretical AnMBR directly coupled to a public toilet. The combined system would be capable of recycling its water for use in toilet flushing and would be capable of providing enough energy to power both the toilet and AnMBR operation. The addition of food waste to the feed would help to ensure process stability and energy production by the AnMBR. Ammonia accumulation within the system would have to be managed through struvite precipitation, ion exchange, oxidation, plant uptake or other means. Generated biogas can be converted into heat and/or electricity using small scale gas generators. AnMBR technology has high potential for success in slum settings, if considerations for maintenance and supplies are made as part of the design and system delivery.