Excess biomass being removed.
Excess biomass being removed.

Economic growth does not always bring with it immediate sanitary improvements and waterborne illnesses are still far too common. Not only that, but traditional wastewater treatment facilities have high operational costs and are big users of energy.

In spite of the impressive growth by former third world countries such as India, problems posed by waterborne pathogens still cause about 80% of illnesses. A huge part of this effort is the development of wastewater treatment facilities. Long bedeviled by poor access to the energy needed to operate wastewater treatment systems, only 20% of communities in India had access to wastewater treatment in the past.

New technology

Now, a new technology developed by Aquanos Energy Ltd, and further enhanced by World Water Works, is now available and promises to produce a high quality effluent at a fraction of the total energy consumption of conventional wastewater treatment plants.

The new technology captures and harnesses the symbiotic relationship between bacteria and algae. This natural process results in a 90% reduction in plant energy, reduces a wastewater treatment system’s operational costs by 40-60%, and reduces capital expenditures. Its manufacturers claim that it is far more sustainable than other biological wastewater treatment systems that use microorganisms to treat wastewater, so it is ideal for use in India and other energy-constrained countries.

The process has been proven in a demonstration project and is now being launched to the municipal market in India and Africa. Further enhancements are already on the horizon, including an enhanced nutrients removal system and resource harvesting of the algae for use as a fertilizer and other useful products.

Biological wastewater treatment
 

In most conventional intensive wastewater treatment operations, organic material and nitrogenous compounds are degraded by aerobic microorganisms (bacteria), which require large amounts of oxygen for their biochemical activity. Supplying this oxygen usually requires mechanical devices, like surface aerators and air compressors and blowers to introduce air into the reactors. These devices use huge amounts of electrical power. About 60% of the energy consumed by treating water comes from blowing oxygen into the wastewater. The associated power costs impose a significant (sometimes insurmountable) financial burden on communities, making wastewater treatment effectively impossible for many communities in India and Africa.

Several years ago, engineers at Aquanos began looking for a better, more sustainable method, and one that would extend the benefits of advanced wastewater treatment to countries that lacked affordable energy alternatives. They noted that water is the single largest factor in world energy consumption, including water treatment, supply, purification, and wastewater. It is also the major cause of disease in these countries, and they knew it was possible to solve that problem. But perhaps most importantly, they wanted to find a way to change the way wastewater is viewed. Rather than thinking of wastewater as simply dirty water, the Aquanos team saw wastewater as a resource from which nutrients could be derived or converted to energy and products.

Recognizing that eliminating the need to blow air into the wastewater would significantly reduce energy needs, they examined a few alternatives, eventually alighting on the plan to use algae, an aquatic plant that consumes CO2 from water and produces oxygen. Bacteria supplies carbon dioxide to the algae, algae provides oxygen to the bacteria, and both remove impurities from wastewater.

Production of oxygen by algae is not a new idea – it has been used extensively in wastewater treatment, either in conventional waste stabilization ponds or the more engineered high-rate algae ponds. However, these lagoon-based algae wastewater treatment systems require large areas of land because the algae ponds have to be very shallow so they receive enough sunlight. Such systems are also not highly-controllable systems, resulting in inconsistent effluent quality.

Mixing the oxygen-producing algae with the oxygen-consuming bacteria in a single environment turns out to create conditions that are not optimal for either type of organism. For example, the presence of large numbers of microorganisms creates high turbidity, which turns water brown, thus obscuring the sunlight the algae need to grow. Because of these issues, many systems that started out using algae to produce oxygen had moved into forced aeration – with its high energy use.

Separating oxygen

Aquanos engineers devised a novel approach that uses algae to produce the oxygen required for aerobic wastewater treatment, which then takes place on a fixed-film system. The unique aspect of the new patent pending approach is that it uses two separate reactors to separate the oxygen production capabilities of algae from the bacterial oxidation of both organic and nitrogenous compounds that occur on an attached-growth aerobic system.

In this process, biological oxidation is achieved on an attached biomass, by recycling an oxygen-rich algae stream through a moving bed biofilm reactor (MBBR), resulting in a high quality effluent and a controllable process and one that requires a fraction of the energy required for aeration with mechanical aeration or blowers, and considerably less space than traditional extensive algae-based systems.

The algae-growing pond is shallow, so light can penetrate it. The retained microorganisms are in a different reactor close by, so there can be high concentrations of microorganisms without interfering with the algae. A pump transfers the highly oxygenated water into the fixed film reactor. Energy use could be further reduced if a solar pump was used to transfer the oxygenated water.

In addition, algae produced during this process can be used by local farms or urban developments as slow release nitrogen and phosphorus fertilizer. With additional treatment, the algal biomass could be used for the production of animal feed and possibly other high value algae-derived products.

This natural process results in a 90% reduction in plant energy, reduces a wastewater treatment system’s operational costs by 40-60%, and significantly reduces capital expenditures. In some circumstances it will produce a net-positive energy balance. In addition, the method is considered a carbon sequestering technology, capturing greenhouse gases (CO2) rather than releasing them to the atmosphere.

The process basics

In the process developed by Aquanos, wastewater is screened and de-gritted before being introduced into an anaerobic stage. Depending on the application, this may be anything from a simple lined earthen anaerobic lagoon to a fully engineered anaerobic sludge blanket reactor. This stage reduces organic loading, and serves as a sink for excess biomass.

Following the anaerobic stage, the wastewater is introduced into the MBBR, where aerobic chemical oxygen demand (COD) removal and nitrification take place. The active biomass is grown as a biofilm on small, cylindrical HDPE elements designed to maximize protected surface area and mass transfer of substrates and oxygen from the bulk liquid into the biofilm. MBBR provides a ‘home’ in which the bacteria can live and be concentrated and protected. The process is also very forgiving, handles load swings easily, and is simple to operate. The algae are harvested using an AHTO® (Algae Harvesting Technology Optimized) system.

The MBBR and AHTO components for the Aquanos system were designed in close consultation with World Water Works, a global leader in MBBR and AHTO that has installed numerous wastewater treatment plants using MBBR and AHTO technologies. The two companies further enhanced and optimized the Aquanos process using World Water Works’ proprietary MBBR and AHTO technologies.

Unlike activated sludge, the biomass carriers (with the active biomass) are retained within the reactor by sieves, and only excess biomass, shorn off the biomass carriers, is carried over to the final solids-separation system (clarifier, dissolved air flotation unit, or filter) with the effluent. The use of an attached growth system, where the biomass is physically confined and does not flow through the system, allows the oxygen-rich algal liquid to flow through the system with minimal mixing of algae and bacterial mass. This minimizes contamination of the algal raceway with bacterial biomass and flocculent mass (flocs), reducing turbidity and shading of the algae, and ultimately improving the algae’s environmental conditions.

The MBBR stage may be operated with a single reactor, a few reactors in series, or parallel reactors – depending on the degree of biological oxygen demand (BOD) removal or nitrification desired. The MBBRs are equipped with mechanical mixers to ensure carrier mixing and optimal mass transfer of substrates.

Oxygen to the MBBR is supplied by algae-rich water located in open raceway reactors. The area, number, and staging of the raceway reactors depends on the process characteristics and amount of oxygen required. The oxygen-rich liquid is recirculated to the MBBR using high-flow, low-head pumps; from the MBBR the now oxygen-depleted liquid is returned to the raceway, where it can begin producing oxygen again. Final effluent is conveyed either from the MBBR or from the raceway to a final solids-separation unit, where the AHTO is incorporated to separate the algae. Excess biomass (algae and bacteria) is removed from this stage for further processing, either in the digester, or for production of fertilizer, animal feed, or, in the future, biofuel.

The anaerobic and aerobic segments are sized according to standard design procedures. During development of the system, Aquanos engineers experimented with algae raceway sizing and staging, and found that raceway ponds with hydraulic retention times of 24 hours were sufficient for full BOD removal.

Proven concept

Aquanos began testing the concept in a pilot plant in a sidestream of the Ra’anana Municipal Wastewater Treatment Plant in Israel. They pumped screened and degritted municipal wastewater from the plant influent channel to the pilot plant at a rate of about 3 l3 per day. The process piloted successfully for 18 months, producing 20-20 water (less than 20 ppm of BOD, and less than 20 ppm of TSS (total suspended solids)), with negligible energy consumption.

The pilot showed that it is possible to treat municipal wastewater aerobically without mechanical aeration, while supplying oxygen to the aerobic process through an oxygen-rich stream of algae. With sufficient dissolved oxygen (DO) maintained within the system, the pilot plant consistently produced soluble pollutant removal rates equivalent to those found in conventional systems with mechanical aeration.

After the success of the pilot project, Aquanos collaborated with World Water Works to develop, optimize, and implement the design for a larger (50 l3per day) demonstration project at a sidestream of the much larger Dan Region Wastewater Treatment Plant (Shafdan), in Israel. Construction of the demonstration project began in June 2013 and the plant has been operating smoothly for several months as it builds biomass.

The demonstration system will continue to be used to study biological nutrient removal for nitrogen and phosphorous, improving solids separation, and reusing the separated biomass for anaerobic digestion or production of reusable end products, including fertilizers and plant growth enhancers. In the future, production of biofuel may also be considered.

A full scale system could be anywhere from 20 gallons per minute (gpm) to 10,000 gpm, with an optimum size probably around 3600 gpm. The system is most appropriate for larger, greenfield sites; since algae needs sunlight, the tank is only 18 in deep, covering a large amount of surface area to get the necessary footprint.

While the large land area needed somewhat limits the use of the technology in the US, the system is also a solution for certain industries with high ammonia and phosphorus, for example, CAFO (concentrated animal feed operations), food and beverage plants, and tanneries.

Spreading the word

Algae need sunlight to grow, so the system Aquanos developed is most applicable to sunny and warm climates. Plans are now underway to launch the Aquanos system to the municipal market in India and Africa, offering it as a way to deliver wastewater treatment to urban and suburban communities that have very little energy. Technology that would clean up wastewater, not use much energy, and produce a fertilizer that can be used locally, is a powerful concept.

Compared to other activated sludge and highly energy intensive processes, which leave you with wastes that have to be hauled, this low cost sustainable technology has the potential to rapidly increase the population of India that has wastewater treatment from its existing 20% to much closer to the US’s rate of 90%.

In addition, Aquanos and World Water Works are currently working on broadening the patent with process trains and optimized treatment to generate a monoculture, harvesting fertilizer, animal feed, bioplastics, and biofuels. The algae consume nitrogen and phosphorous from water – and these are expensive commodities. The team’s ultimate vision is to obtain wastewater from one side of the process and biofuel from the other side, along with clean water.

The new process has two distinct layers of benefits. The first is that it is truly a cost efficient technology that reduces capital expenditures and energy/operational expenditures, while producing high quality effluent. The second is its ability to facilitate harvesting resources, in the form of biogas and other high value products.

In the long run, the development of a much cheaper wastewater stream that includes the sale of harvested resources will be a game changer. Instead of simply spending money on wastewater, people can make a profit from it – making the Aquanos system a truly revolutionary approach.
 

AHTO®  is a registered trade mark of Aquanos Energy Ltd