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

Summary

An experimental methodology is presented to compare the performance of small (100 L) and large (1,000 L) scale reactors designed for algae remediation of landfill wastewater. System characteristics, including surface area to volume ratio, retention time, biomass density, and wastewater feed concentrations, can be adjusted based on application.

Abstract

An experimental methodology is presented to compare the performance of two different sized reactors designed for wastewater treatment. In this study, ammonia removal, nitrogen removal and algal growth are compared over an 8-week period in paired sets of small (100 L) and large (1,000 L) reactors designed for algal remediation of landfill wastewater. Contents of the small and large scale reactors were mixed before the beginning of each weekly testing interval to maintain equivalent initial conditions across the two scales. System characteristics, including surface area to volume ratio, retention time, biomass density, and wastewater feed concentrations, can be adjusted to better equalize conditions occurring at both scales. During the short 8-week representative time period, starting ammonia and total nitrogen concentrations ranged from 3.1-14 mg NH₃-N/L, and 8.1-20.1 mg N/L, respectively. The performance of the treatment system was evaluated based on its ability to remove ammonia and total nitrogen and to produce algal biomass. Mean ± standard deviation of ammonia removal, total nitrogen removal and biomass growth rates were 0.95±0.3 mg NH₃-N/L/day, 0.89±0.3 mg N/L/day, and 0.02±0.03 g biomass/L/day, respectively. All vessels showed a positive relationship between the initial ammonia concentration and ammonia removal rate (R²=0.76). Comparison of process efficiencies and production values measured in reactors of different scale may be useful in determining if lab-scale experimental data is appropriate for prediction of commercial-scale production values.

Introduction

Translation of bench-scale data to larger scale applications is a key step in the commercialization of bioprocesses. Production efficiencies in small-scale reactor systems, particularly those focusing on the use of microorganisms, have been shown to consistently over predict efficiencies occurring in commercial-scale systems ^1,2,3,4. Challenges also exist in scaling up photosynthetic cultivation of algae and cyanobacteria from the laboratory scale to larger systems for the purpose of manufacturing high-value products, such as cosmetics and p....

Protocol

1. System Setup

Note: A 'paired system' refers to one aquarium tank and one raceway pond, run in parallel.

1. For one paired system, use one 100 L aquaria tanks (AT), with an overhead mixer for the small-scale vessel, and one 1,000 L raceway pond (RWP), with a paddle wheel mixer for the large-scale vessel. Vessels used in this system are pictured in Figure 1.
2. Inoculate all vessels with the same algae culture. Use a high density of the inoculation, resulting in a final density of no less than 0.1 g/L once diluted to the full volume in the tank or pond ¹⁰. It may take a considerable amount of time (weeks....

Results

The aim of this study is to compare the biomass growth and nutrient removal capabilities of algal cultures grown in small- and large-scale reactors. This study uses two paired systems, referred to as System 1 and System 2, to duplicate its findings. These representative results are from an 8-week period, February through April, 2016. The first raceway pond was inoculated with algae originally sourced from an outdoor pond in Philadelphia, PA ¹⁴. This culture was gro.......

Discussion

System performance:

Over the course of an 8-week study, the productivity of the small- and large-scale vessels in a system were compared. In this study nitrogen and ammonia removal rates and biomass growth rates were used as measures of productivity of the treatment system. The system was operated as a semi-batch reactor, where each week was operated under discrete conditions. Representative results account for the first 8 weeks of system operation, however a full study would extend for much long.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Aquarium Tank			Any 100+ L aquarium tank with optically clear glass can be used
RW 3.5	MicroBio Engineering		Raceway Pond
Eurostar 100 digital	IKA	4238101	Overhead mixers
Leachate	Sandtown Landfill
Sampling Bottles	Nalgene		Plastic or glass, lab grade, 125-200 mL
Transfer Pumps			Garden type pump with drinking water quality hoses will be suitable
AmVer Salicylate Test 'N Tube	Hach	2606945	High Range Ammonia Tests
NitraVer X Nitrogen - Nitrate Reagent Set	Hach	2605345	High Range Nitrate Tests
NitriVer 2 Nitrite Reagent Powder Pillows	Hach	2107569	High Range Nitrite Tests
Hach DR2400 Spectrophotmeter	Hach		The DR2400 was discontinued, but any DR series Hach spectrophotometer can be used in this application.
EMD Microbiological Analysis Membrane Filters	Millipore	HAWG047S6	0.45 µm filters