Feasibility of organic micropollutant removal from municipal wastewaters by algal treatment vs. activated sludge treatment: Comparison based on non-targeted organic compound analysis.

Sustainability and life-cycle concerns about the conventional activated sludge (CAS) process for wastewater treatment have been driving the development of energy-efficient, greener alternatives. Feasibility of an algal-based wastewater treatment (A-WWT) system has been demonstrated recently as a possible alternative, capable of simultaneous nutrient and energy recovery. This study compared capabilities of the A-WWT and CAS systems in removing organic micropollutants (OMP).

Domestic wastewater sludge valorization: Multi-criteria evaluation of anaerobic digestion vs. hydrothermal liquefaction.

The emerging hydrothermal liquefaction (HTL) process is evaluated against the classical anaerobic digestion (AD) processes for stabilizing wastewater sludges and recovering their energy- and nutrient-contents. Although HTL affords faster stabilization, better process stability, and liquid fuel and sterile fertilizer recovery, it suffers from higher energy demand and lower technology readiness level. For a rational comparison of these pathways, a multi-criteria evaluation is conducted considering 21 technical, environmental, economic, and social criteria.

Feasibility of ammonium sulfate recovery from wastewater sludges: Hydrothermal liquefaction pathway vs. anaerobic digestion pathway.

This study evaluated two pathways to recover the nitrogen-content of wastewater sludges as ammonium sulfate (AmS) for use as fertilizer. The first pathway entails sludge stabilization by hydrothermal liquefaction (HTL) followed by recovery of AmS from the resulting aqueous product by gas permeable membrane (GPM) separation. The second one entails stabilization of the sludges by anaerobic digestion (AD) followed by recovery of AmS from the resulting centrate by GPM separation.

Life cycle energy use and greenhouse gas emissions for a novel algal-osmosis membrane system versus conventional advanced potable water reuse processes: Part I.

This study applied a life cycle assessment (LCA) methodology for a comparative environmental analysis between an innovative algae resource recovery and near zero-liquid discharge potable reuse system (i.e., the main system) versus a conventional potable reuse system (i.

Techno-economic assessment of a novel algal-membrane system versus conventional wastewater treatment and advanced potable reuse processes: Part II.

This study developed a comprehensive techno-economic assessment (TEA) framework to evaluate an innovative algae resource recovery and near zero-liquid discharge potable reuse system (i.e., the main system) in comparison with a conventional potable water reuse system (i.

Impacts of seasonality and operating conditions on algal-dual osmosis membrane system for potable water reuse: Part 2.

This study investigated the impact of seasonal variation and operating conditions on recovery of potable quality water from municipal wastewater effluent using an integrated algal treatment process with a dual forward osmosis (FO)-reverse osmosis (RO) membrane system. Pilot study of the algal process treating primary effluent validated the technical viability and seasonal performance during warm weather (May to October, 25-55 °C) using an extremophilic algal strain Galdieria sulphuraria, and during cold weather (November to April, 4-17 °C) using polyculture strains of algae and bacteria. Algal effluents from both seasons were used as the feed solution for the laboratory FO-RO study.

Impacts of seasonality and operating conditions on water quality of algal versus conventional wastewater treatment: Part 1.

Municipal wastewater is a reliable source from which water, renewable energy, and nutrients could be recovered for beneficial use. Our previous efforts have documented that an innovative algal-based wastewater treatment (WWT) system could recover energy and nutrients from wastewater while having a lower energy footprint than conventional WWT processes. As a biological treatment process, the algal WWT can be affected by algal species, operating conditions, and meteorological factors.

Biofertilizer recovery from organic solid wastes via hydrothermal liquefaction.

Hydrothermal liquefaction (HTL) has emerged as a viable pathway for processing wet organic solid wastes (OSW) to yield biocrude oil which could be upgraded to transportation fuels and specialty chemicals. The HTL process results in two byproducts laden with high levels of carbon, nitrogen, and phosphorous. Recovery of phosphates in the byproducts as struvite and ammoniacal-nitrogen (NH-N) as ammonium sulfate is proposed here as a promising pathway to utilize the HTL byproducts.

Metagenomic profiling of antibiotic resistance and virulence removal: Activated sludge vs. algal wastewater treatment system.

Conventional activated sludge-based (CAS) wastewater treatment plants are known to be a source of antibiotic resistance genes (ARGs) and virulence genes (VGs). As an alternative, a single-step mixotrophic algal wastewater treatment (A-WWT) system is proposed here to effectively reduce ARGs and VGs in the final effluent while meeting all the discharge standards. In this study, we applied the metagenomic profiling approach to compare the A-WWT system against the CAS system in terms of removal efficacy of ARG and VGs.

Pilot Demonstration of Reclaiming Municipal Wastewater for Irrigation Using Electrodialysis Reversal: Effect of Operational Parameters on Water Quality.

The modification of ion composition is important to meet product water quality requirements, such as adjusting the sodium adsorption ratio of reclaimed water for irrigation. Bench- and pilot-scale experiments were conducted using an electrodialysis reversal (EDR) system with Ionics normal grade ion-exchange membranes (CR67 and AR204) to treat the reclaimed water in the Scottsdale Water Campus, Arizona. The goal is to investigate the impact of operating conditions on improving reclaimed water quality for irrigation and stream flow augmentation.

Techno-economic optimization of phosphorous recovery in an algal-based sewage treatment system.

Previous reports have documented the technical viability of an algal pathway for treating primary effluent and recovering its phosphorus-content (P) via hydrothermal liquefaction (HTL) of the resulting biomass. In this pathway, leaching P from HTL-derived biochar was found as the critical step impacting the economics of P-recovery. As such, a process model was developed in the current study to optimize P leaching from biochar as a function of five parameters.

Bacteria and virus reduction in secondary treatment: Potential for minimizing post disinfectant demand.

Today's wastewater utilities are facing the dilemma of balancing pathological threats of bacteria and viruses in their effluent against health threats associated with the byproducts of disinfection. A possible solution to this dilemma is to adopt secondary treatment technologies capable of concurrent pathogen reduction, minimizing the demand for external disinfectants. Towards this end, bacterial and viral reductions possible in algal wastewater treatment (WWT) systems are highlighted here and compared with those in conventional activated sludge (AS) systems and membrane bioreactor (MBR) systems.

Removal and recovery of nutrients from municipal sewage: Algal vs. conventional approaches.

This paper presents a pilot scale study of an algal-based sewage treatment and resource recovery (STaRR) system capable of treating municipal sewage and recovering its nitrogen- and phosphorous-content as fertilizer. Core components of the STaRR system include i) mixotrophic cultivation of algal biomass in settled sewage; ii) hydrothermal liquefaction (HTL) of the resulting algal biomass, and iii) processing of the products of HTL to recover energy in the form of biocrude and nutrients in the form of struvite. Performance of a pilot-scale STaRR system in recovering nitrogen (N) and phosphorus (P) from settled sewage as struvite is documented and compared with that of existing and emerging technologies.

Removal of antibiotic resistance genes in an algal-based wastewater treatment system employing Galdieria sulphuraria: A comparative study.

In this study, we compared removal of antibiotic resistant bacteria (ARB) and antibiotic resistant genes (ARGs) in two wastewater treatment systems fed with the same primary effluent: a conventional wastewater treatment system (consisting of a trickling filter followed by an activated sludge process) versus an algal-based system, employing an extremophilic alga, Galdieria sulphuraria. Our results demonstrated that the algal system can reduce concentrations of erythromycin- and sulfamethoxazole-resistant bacteria in the effluent more effectively than the conventional treatment system. A decreasing trend of total bacteria and ARGs was observed in both the treatment systems.

Potable-quality water recovery from primary effluent through a coupled algal-osmosis membrane system.

A coupled algal-osmosis membrane treatment system was studied for recovering potable-quality water from municipal primary effluent. The core components of the system included a mixotrophic algal process for removal of biochemical oxygen demand (BOD) and nutrients, followed by a hybrid forward osmosis (FO)-reverse osmosis (RO) system for separation of biomass from the algal effluent and production of potable-quality water. Field experiments demonstrated consistent performance of the algal system to meet surface discharge standards for BOD and nutrients within a fed-batch processing time of 2-3 days.

Bio-crude oil from hydrothermal liquefaction of wastewater microalgae in a pilot-scale continuous flow reactor.

To explore the feasibility of scaling up hydrothermal liquefaction (HTL) of algal biomass, a pilot-scale continuous flow reactor (CFR) was operated to produce bio-crude oil from algal biomass cultivated in urban wastewater. The CFR system ran algal slurry (5 wt.% solids loading) at 350 °C and 17 MPa for 4 h without any clogging issues.

Hydrothermal liquefaction of Galdieria sulphuraria grown on municipal wastewater.

Two strains of Galdieria sulphuraria algae, 5587.1 and SOOS, were grown on municipal wastewater to develop energy-positive treatment systems. Hydrothermal liquefaction (HTL) of 5-10 wt% algal biomass solids was conducted at 310-350 °C for 5-60 min to produce bio-crude oil.

Hydrothermal liquefaction of high- and low-lipid algae: Mass and energy balances.

Hydrothermal liquefaction (HTL) of high-lipid microalgae Nannochloropsis salina (N. salina) and low-lipid microalgae Galdieria sulphuraria (G. sulphuraria) were run under subcritical conditions (310-350 °C and 10-17 MPa) in a 1.

Hydrothermal liquefaction of Cyanidioschyzon merolae and the influence of catalysts on products.

This work investigates the hydrothermal liquefaction (HTL) of Cyanidioschyzon merolae algal species under various reaction temperatures and catalysts. Liquefaction of microalgae was performed with 10% solid loading for 30min at temperatures of 180-300°C to study the influences of two base and two acid catalysts on HTL product fractions. Maximum biocrude oil yield of 16.

Algal-based, single-step treatment of urban wastewaters.

Currently, urban wastewaters (UWW) laden with organic carbon (BOD) and nutrients (ammoniacal nitrogen, N, and phosphates, P) are treated in multi-stage, energy-intensive process trains to meet the mandated discharge standards. This study presents a single-step process based on mixotrophic metabolism for simultaneous removal of carbon and nutrients from UWWs. The proposed system is designed specifically for hot, arid environments utilizing an acidophilic, thermotolerant algal species, Galdieria sulphuraria, and an enclosed photobioreactor to limit evaporation.

Algal biofuels from urban wastewaters: maximizing biomass yield using nutrients recycled from hydrothermal processing of biomass.

Recent studies have proposed algal cultivation in urban wastewaters for the dual purpose of waste treatment and bioenergy production from the resulting biomass. This study proposes an enhancement to this approach that integrates cultivation of an acidophilic strain, Galdieria sulphuraria 5587.1, in a closed photobioreactor (PBR); hydrothermal liquefaction (HTL) of the wet algal biomass; and recirculation of the nutrient-rich aqueous product (AP) of HTL to the PBR to achieve higher biomass productivity than that could be achieved with raw wastewater.

Evaluation of a thermo-tolerant acidophilic alga, Galdieria sulphuraria, for nutrient removal from urban wastewaters.

Nutrient removal from primary wastewater effluent was tested using Galdieria sulphuraria, an acidophilic and moderately thermophilic alga. Biomass yield recorded in this study (27.42g biomass per g nitrogen removed) is higher than the average reported in the literature (25.

Evaluation of internally illuminated photobioreactor for improving energy ratio.

The internally illuminated photobioreactor (IIPBR) design has been shown to be more efficient in utilizing the incident light energy than the externally illuminated designs. This study evaluated (i) optimal sparging of the IIPBR with CO2-enriched air (CEA) to enhance biomass productivity; and, (ii) single-stage and two-stage operation of the IIPBR to enhance lipid productivity. Growth data from two algal cultures-Scenedesmus sp.

In situ ethyl ester production from wet algal biomass under microwave-mediated supercritical ethanol conditions.

An in situ transesterification approach was demonstrated for converting lipid-rich wet algae (Nannochloropsis salina) into fatty acid ethyl esters (FAEE) under microwave-mediated supercritical ethanol conditions, while preserving the nutrients and other valuable components in the algae. This single-step process can simultaneously and effectively extract the lipids from wet algae and transesterify them into crude biodiesel. Experimental runs were designed to optimize the process parameters and to evaluate their effects on algal biodiesel yield.

Modeling microalgal growth in an airlift-driven raceway reactor.

In previous proof-of-concept studies, feasibility of a new airlift-raceway configuration and its energetic advantage and improved CO2 utilization efficiency over the traditional raceways and photobioreactors have been documented. In the current study, a mathematical model for predicting biomass growth in the airlift-raceway reactor is presented, which includes supply and transfer of CO2 and the synergetic effects of light, CO2, nitrogen, and temperature. The model was calibrated and validated with data from prototype scale versions of the reactor on two test species: Nannochloropsis salina and Scenedesmus sp.