Comparison of Scale in a Photosynthetic Reactor System for Algal Remediation of Wastewater

The overall goal of this procedure is to evaluate the effect of scale on algal growth and nitrogen removal in a leachate treatment system. This method can help determine how increasing the scale of a system will impact the treatment efficiency. The main advantage of this technique is that it can be adapted for a variety of microbial and wastewater treatment systems.

For this protocol, a paired system refers to one 100 liter aquarium tank and one 1, 000 liter raceway pond run in parallel. Start with a high density inoculum, which may take weeks to months to grow enough algae for. Inoculate all vessels with the same algae culture, ensuring that the final density is no less than 0.1 grams per liter once diluted to the full volume in the tank or pond.

Untreated landfill leachate serves as the nutrient source for this system. Use leachate taken from a landfill that accepts primarily domestic waste and has low levels of toxins. The amount of leachate used in each tank or pond can vary depending on the strength of the wastewater.

Start the aquarium tank with one liter of leachate in 59 liters of water for a 60 liter working volume. Likewise, start the raceway pond with 10 liters of leachate in 590 liters of water for a 600 liter working volume. Week to week, operate the aquarium tank and raceway pond as semi-batch reactors with hydraulic retention times of three weeks.

Monitor environmental conditions, such as air temperature and solar radiation, using a commercial weather station. Also monitor tank or pond conditions, such as water temperature, pH, and dissolved oxygen, using commercial probes and a data logger. At the beginning of each week, take a 125 milliliter sample from each vessel to be tested for biomass density, as well as ammonia-N, nitrate-N, and nitrite-N.

Measure the biomass by a standard total suspended solids protocol using 0.45 micron filters. After weighing the filter paper, filter 20 to 40 milliliters of sample using a vacuum filtration system. Dry the biomass and filter paper in an oven at 105 degrees Celsius for one hour.

After drying, calculate the biomass density. Next, measure ammonia, nitrate, and nitrite using a spectrophotometer and commercial method kits according to the manufacturer's protocol. After one week, take 125 milliliter samples from each vessel and analyze the samples as before.

This is the end of the first week. To prepare for the next week's cycle, pump the entire volume of the aquarium tank into the raceway pond. Remove 1/3 of the volume from the raceway pond.

Replace the volume removed with water and untreated leachate. Then, transfer approximately 60 liters from the raceway pond back into the aquarium tank. This ensures that the aquarium tank and the raceway pond are starting with the same nutrient and biological conditions each week.

In this study, two paired systems were used, referred to as system one and system two, to duplicate the findings. Ammonia removal rate, total nitrogen removal rate, and biomass growth rate were used as metrics to evaluate the treatment system. The rates from system one and system two are shown here for the representative study period.

Data from all vessels over the representative study period showed that ammonia removal trended positively with increasing starting ammonia concentration. Once the system is up and running, reactor parameters, such as biomass density, length of time between mixing, working volume, retention time, and the amount of wastewater added, can be adjusted to better test a customized system. Ultimately, results from this procedure can be used to inform feasibility studies of full scale treatment processes.

For example, the effect of scale on important reactor parameters, such as growth rate and nutrient removal, can be used to verify the accuracy of input data used to simulate full scale production processes and lifecycle assessments and technoeconomic analyses. This is a versatile methodology which can be adapted to study the treatment of a variety of wastewaters.