An official website of the United States government
Algae-based wastewater treatment systems have the potential to reduce the energy cost of wastewater treatment processes by utilizing solar energy for biomass growth and nutrient removal. NH4+-N concentrations as high as 200- 300 mg/L are known to inhibit algae growth. Many research studies on the treatment of centrate after anaerobic digestion have been published recently. However, in these studies the centrate was diluted for the growth of algae due to the high NH4+-N concentrations, which are toxic to algae. Alternative solutions are necessary to treat high NH4+-N strength wastewater without addition of freshwater. Zeolites are natural hydrated aluminosilicate minerals that have been used to reduce ammonium inhibition on microorganisms due to their high affinity for ammonium ions. It is possible to use the ion-exchange (IX) capacity of zeolite to reduce the toxicity of ammonia to algae. Importantly, the zeolite, which becomes saturated with ammonium, can be reused as a slow release fertilizer. The objectives of this research were to evaluate the impact of zeolite dosage on the nutrient removal efficiency for high strength wastewater and develop mathematical models to predict the performance of hybrid IX and algae growth systems with varying doses of zeolite.
more »
« less
Experimental and theoretical investigations of rotating algae biofilm reactors (RABRs): Areal productivity, nutrient recovery, and energy efficiency
Abstract Microalgae biofilms have been demonstrated to recover nutrients from wastewater and serve as biomass feedstock for bioproducts. However, there is a need to develop a platform to quantitatively describe microalgae biofilm production, which can provide guidance and insights for improving biomass areal productivity and nutrient uptake efficiency. This paper proposes a unified experimental and theoretical framework to investigate algae biofilm growth on a rotating algae biofilm reactor (RABR). Experimental laboratory setups are used to conduct controlled experiments on testing environmental and operational factors for RABRs. We propose a differential–integral equation‐based mathematical model for microalgae biofilm cultivation guided by laboratory experimental findings. The predictive mathematical model development is coordinated with laboratory experiments of biofilm areal productivity associated with ammonia and inorganic phosphorus uptake by RABRs. The unified experimental and theoretical tool is used to investigate the effects of RABR rotating velocity, duty cycle (DC), and light intensity on algae biofilm growth, areal productivity, nutrient uptake efficiency, and energy efficiency in wastewater treatment. Our framework indicates that maintaining a reasonable light intensity range improves biomass areal productivity and nutrient uptake efficiency. Our framework also indicates that faster RABR rotation benefits biomass areal productivity. However, maximizing the nutrient uptake efficiency requires a reasonably low RABR rotating speed. Energy efficiency is strongly correlated with RABR rotating speed and DC.
more »
« less
- Award ID(s):
- 1816783
- PAR ID:
- 10418040
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Biotechnology and Bioengineering
- Volume:
- 120
- Issue:
- 10
- ISSN:
- 0006-3592
- Format(s):
- Medium: X Size: p. 2865-2879
- Size(s):
- p. 2865-2879
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Highlights Aquatic vegetation-based nutrient recovery offers an alternate approach for treating agricultural wastewater. Microalgae and duckweed can upcycle waste nutrients into valuable bio-based products. Producing feed, fertilizer, and fuel from manure-grown aquatic vegetation promotes a circular N-bioeconomy. Abstract . The massive amounts of nutrients that are currently released into the environment as waste have the potential to be recovered and transformed from a liability into an asset through photosynthesis, industry insight, and ecologically informed engineering design aimed at circularity. Fast-growing aquatic plant-like vegetation such as microalgae and duckweed have the capacity to enable local communities to simultaneously treat their own polluted water and retain nutrients that underlie the productivity of modern agriculture. Not only are they highly effective at upcycling waste nutrients into protein-rich biomass, microalgae and duckweed also offer excellent opportunities to substitute or complement conventional synthetic fertilizers, feedstocks in biorefineries, and livestock feed while simultaneously reducing the energy consumption and greenhouse gas emissions that would otherwise be required for their production and transport to farms. Integrated systems growing microalgae or duckweed on manure or agricultural runoff, and subsequent reuse of the harvested biomass to produce animal feed, soil amendments, and biofuels, present a sustainable approach to advancing circularity in agricultural systems. This article provides a review of past efforts toward advancing the circular nitrogen bioeconomy using microalgae- and duckweed-based technologies to treat, recover, and upcycle nutrients from agricultural waste. The majority of the work with microalgae- and duckweed-based wastewater treatment has been concentrated on municipal and industrial effluents, with <50% of studies focusing on agricultural wastewater. In terms of scale, more than 91% of the microalgae-based studies and 58% of the duckweed-based studies were conducted at laboratory-scale. While the range of nutrient removals achieved using these technologies depends on various factors such as species, light, and media concentrations, 65% to 100% of total N, 82% to 100% of total P, 98% to 100% of NO3-, and 96% to 100% of NH3/NH4+ can be removed by treating wastewater with microalgae. For duckweed, removals of 75% to 98% total N, 81% to 93% total P, 72% to 98% NH3/NH4+, and 57% to 92% NO3- have been reported. Operating conditions such as hydraulic retention time, pH, temperature, and the presence of toxic nutrient levels and competing species in the media should be given due consideration when designing these systems to yield optimum benefits. In addition to in-depth studies and scientific advancements, policies encouraging supply chain development, market penetration, and consumer acceptance of these technologies are vitally needed to overcome challenges and to yield substantial socio-economic and environmental benefits from microalgae- and duckweed-based agricultural wastewater treatment. Keywords: Circular bioeconomy, Duckweed, Manure treatment, Microalgae, Nitrogen, Nutrient recycling, Wastewater treatment.more » « less
-
Abstract Shifts in plant functional groups associated with climate change have the potential to influence peatland carbon storage by altering the amount and composition of organic matter available to aquatic microbial biofilms. The goal of this study was to evaluate the potential for plant subsidies to regulate ecosystem carbon flux (CO2) by governing the relative proportion of primary producers (microalgae) and heterotrophic decomposers (heterotrophic bacteria) during aquatic biofilm development in an Alaskan fen. We evaluated biofilm composition and CO2flux inside mesocosms with and without nutrients (both nitrogen and phosphorus), organic carbon (glucose), and leachates from common peatland plants (moss, sedge, shrub, horsetail). Experimental mesocosms were exposed to either natural sunlight or placed under a dark canopy to evaluate the response of decomposers to nutrients and carbon subsidies with and without algae, respectively. Algae were limited by inorganic nutrients and heterotrophic bacteria were limited by organic carbon. The quality of organic matter varied widely among plants and leachate nutrient content, more so than carbon quality, influenced biofilm composition. By alleviating nutrient limitation of algae, plant leachates shifted the biofilm community toward autotrophy in the light-transparent treatments, resulting in a significant reduction in CO2emissions compared to the control. Without the counterbalance from algal photosynthesis, a heterotrophic biofilm significantly enhanced CO2emissions in the presence of plant leachates in the dark. These results show that plants not only promote carbon uptake directly through photosynthesis, but also indirectly through a surrogate, the phototrophic microbes.more » « less
-
A hybrid algal photosynthesis and ion exchange (HAPIX) process was developed that uses natural zeolite (chabazite) and wild type algae to treat high ammonium strength wastewater. In the HAPIX process, ammonium ions are temporarily adsorbed from the liquid, which reduces the free ammonia concentration below the inhibitory level for algal growth. The slow release of adsorbed NH4+ subsequently supports the continuous growth of algae. In this study, a HAPIX reactor reduced NH4+-N concentrations in centrate from an anaerobic digester from 1,180 mg/L to below 10 mg/L without dilution. Chabazite doses of 60 g/L produced more biomass, with higher protein and starch contents, than doses of 150 g/L and 250 g/L. Approximately 67-70% of fatty acids in the biomass harvested from HAPIX reactors were unsaturated. A mathematical framework that couples a homogeneous surface diffusion model with a co-limitation algal kinetic growth model reasonably predicted the biomass production and NH4+-N concentrations in the HAPIX reactors. The HAPIX process has the potential to serve a two-fold purpose of high NH4+-N strength wastewater treatment and agricultural or commercial biopolymer production.more » « less
-
Autotrophic and heterotrophic microbes in stream biofilms dominate biogeochemical cycling and rely on nutrient and energy resources for growth and productivity. In the boreal forest, variation in these resources can originate from permafrost distribution and controls competition for nutrients between stream autotrophs and heterotrophs. We investigated which resources control nutrient uptake and metabolism in headwater stream biofilms of subarctic Alaska, USA, and how resource availability affects competition for inorganic nutrients. We hypothesized that the competitive outcome between autotrophs and heterotrophs for inorganic nutrients would be dependent on availability of organic C, or inorganic nutrients (N and P). To test our hypotheses, we measured resource limitation at the patch and reach scales along a permafrost gradient in interior Alaska. At the patch scale, nutrient diffusing substrata revealed that, secondary to light, N and P were colimiting to autotrophic growth, whereas C was primarily limiting to heterotrophic respiration. In the presence of labile C, heterotrophs exhibited a larger response to nutrient enrichment and outcompeted autotrophs for inorganic nutrients. At the reach scale, light availability had the largest influence on nutrient uptake, but inorganic nutrients were also important. The positive response to increased nutrient and C availability at the patch scale suggests that the predicted increase in exports into fluvial networks with permafrost degradation will alter biofilm structure and function. Ultimately, biofilm communities will shift to more heterotroph-dominated patches if heterotrophs outcompete autotrophs for inorganic nutrients. As permafrost thaws and nutrients and organic C mobilize into streams, nutrient uptake dynamics and competition within biofilms will be altered, affecting nutrient use and export.more » « less
