A-Stage process - Challenges and drawbacks from lab to full scale studies: A review

Leveraging primary effluent- and glycerol-driven partial denitrification-anammox within a pilot-scale tertiary step-feed moving bed biofilm reactor treating high-rate activated sludge systems effluent

This study investigated the possibility of utilizing primary effluent (PE) carbon as an internal carbon source to drive tertiary partial denitrification-anammox (PdNA) for treating high-rate activated sludge (HRAS) system effluent, so as to offset the consumption of external carbon such as glycerol. This pilot study was conducted in a tertiary step-feed moving bed biofilm reactor (MBBR) over 478 days, using full-scale HRAS secondary effluent as the influent. Unlike most PdNA applications that rely on the expensive supplemental carbon like methanol or glycerol, this study is the first to demonstrate that PE carbon can be utilized as a naturally available carbon source within wastewater to drive PdNA. By taking advantage of this free internal carbon source to driven PdNA, 63% to 74% savings in PE carbon consumption and ∼36% offset in glycerol consumption were achieved. Additionally, glycerol-driven PdNA further reduced both supplemental carbon and aeration energy demands by 70% and 18%. Mechanistic insights from in-situ and ex-situ batch tests revealed that the PE-driven PdNA was facilitated by an anammox-driven nitrite sink, a novel observation that allowed stable PdNA performance without nitrite accumulation. Furthermore, batch tests indicated that endogenous respiration could support PdNA. These findings highlight the potential of applying PE-driven PdNA in full-scale facilities, ushering in a new era of mainstream anammox applications in wastewater treatment, as PdNA is no longer reliant on costly external carbon addition.

Performance of a high-rate activated sludge-integrated vertical-flow constructed wetland for municipal wastewater treatment

High-rate activated sludge (HRAS) coupled with constructed wetland (CW) processes is attracting growing interest in the carbon emissions reduction of wastewater treatment. However, the service effectiveness of CW for low-carbon performance of the HRAS-CW process is still vague, particularly in treating low carbon-to-nitrogen ratio municipal wastewater. In this study, a pilot-scale HRAS-integrated vertical-flow CW (HRAS-IVCW) demonstration plant was established to investigate its performance with respect to water quality, energy consumption and carbon emissions. Through the improved function of CWs, the HRAS-IVCW system achieved satisfactory treatment performance under influent conditions of low organic loading. Moreover, the electrical energy consumption for HRAS-IVCW system operation was 193.2 ± 6.2 mL CH4/g COD, and 32.8 % could be compensated by energy recovery from excess sludge containing high organic content. In addition, an optimized redox environment in the IVCW module using dissolved oxygen allocation and metal oxide addition improved the element flow path and effectively enhanced the simultaneous nutrient removal and carbon emissions of the HRAS-IVCW system, resulting in 8.1-82.3 % lower carbon emissions than those of a similar process under equal TN removal. This study advances the practical application of the HRAS-CW process in the low-carbon design and operation of municipal wastewater treatment plants.

Making waves: Reevaluating iron dosing for carbon recovery in mainstream wastewater treatment system

Wastewater treatment plants face significant challenges in shifting from energy-intensive operations to carbon-neutral, energy-efficient systems. One promising strategy is the iron-enhanced primary treatment process (Fe-CEPT), which focuses on capturing organic carbon for energy recovery rather than biological oxidation. However, while Fe-CEPT has been implemented in wastewater treatment, its potential effects on downstream processes have often been overlooked. This viewpoint takes a comprehensive look at iron dosing for carbon recovery in mainstream wastewater treatment systems. Fe-CEPT has proven effective at capturing particulate organics and phosphorus. However, it is less successful in removing soluble organic carbon. Additionally, the high iron content in sludge, typically between 100 to 200 mg Fe/g SS, has been shown to severely inhibit methane production. This finding contrasts with earlier studies that suggested iron could enhance methane production. It was found the elevated iron levels bind around 20 % of the carbon in the sludge, limiting its bioavailability. These findings indicate that coupling Fe-CEPT with anaerobic digestion may not be an effective method for carbon recovery. A more promising approach that involves limiting iron dosing to less than 10 mg Fe/L in a high-rate activated sludge (HRAS) system is proposed. This strategy combines the benefits of iron dosing and HRAS system, offering a potential pathway to enhance carbon recovery, improve phosphorus management, and reduce the environmental impact of wastewater treatment processes.

Pure water and resource recovery from municipal wastewater using high-rate activated sludge, reverse osmosis, and mainstream anammox: A pilot scale study

In response to the escalating global water scarcity and the high energy consumption associated with traditional wastewater treatment plants, there is a growing demand for transformative wastewater treatment processes that promise greater efficiency and sustainability. This study presents an innovative approach for municipal wastewater treatment that integrates high-rate activated sludge with membrane bio-reactor (HRAS-MBR), reverse osmosis (RO) and partial nitrification-anammox (PN/A). With an influent of 8.4 m³/d, the HRAS-MBR demonstrated a removal efficiency of approximately 85 % for chemical oxygen demand (COD), with over 70 % of it being recovered for energy production. The RO system achieved a recovery rate of 75 % for the influent, producing pure water with an electrical conductivity of 50 μS/cm. Concurrently, it concentrated ammonia, thereby enhancing the effectiveness of the PN/A process for nitrogen removal in the mainstream, resulting in a removal efficiency exceeding 85 %. Notably, the HRAS-MBR achieved significant phosphorus removal without chemical additives, attributed to the presence of influent calcium and magnesium ions. Overall, this integrated system reduced the net energy consumption for reclaimed water production by about 26 % compared to conventional methods. Additionally, the new process produced a revenue of 0.75 CNY/m³, demonstrating considerable economic and environmental benefits. This pilot-scale study offers a viable alternative for wastewater treatment and water reuse in water-scarce regions, contributing to sustainable water resource management.

Seasonal tourism's impact on wastewater composition: Evaluating the potential of alternating activated adsorption in primary treatment

Primary treatment processes have gained attention in recent research and development due to their potential for redirecting carbon towards anaerobic digestion, which can subsequently be used for the production of biomethane. The alternating activated adsorption (AAA) process is implemented on full-scale at several wastewater treatment plants across Europe. However, there is a lack of full-scale studies of advanced carbon capture technology implementations in literature. This study demonstrates the ability of a full-scale AAA process to remove and redirect carbon in a region heavily influenced by tourism. Periods in high and off-season were compared to study the impact of tourism on the composition of the wastewater and the AAA-process. The wastewater characteristics of the high season differed significantly from the low season. During the high season, the PE increased by 37 %, total suspended solids went up by 75 % and chemical oxygen demand increased by 58 %, compared to the low season. Additionally, 80 % of the low volatile lipophilic substances (LVLS) measured were attributed to the impact of tourism. A mass-balance of primary treatment for chemical oxygen demand (COD) and LVLS was conducted for both trial periods. The primary treatment was able to eliminate 56 % of the COD and 62 % of the LVLS in the non-tourist season and 53 % of the COD and 54 % of the LVLS in the tourist season. The increased wastewater load was effectively managed in the AAA-process. Key process parameters like sludge settling characteristics, hydraulic retention time and total suspended solids removal rates remained stable during the high season in winter.

Side-Stream Enhanced Biological Phosphorus Removal (S2EBPR) enables effective phosphorus removal in a pilot-scale A-B stage shortcut nitrogen removal system for mainstream municipal wastewater treatment

While the adsorption/bio-oxidation (A/B) process has been widely studied for carbon capture and shortcut nitrogen (N) removal, its integration with enhanced biological phosphorus (P) removal (EBPR) has been considered challenging and thus unexplored. Here, full-scale pilot testing with an integrated system combining A-stage high-rate activated sludge with B-stage partial (de)nitrification/anammox and side-stream EBPR (HRAS-P(D)N/A-S2EBPR) was conducted treating real municipal wastewater. The results demonstrated that, despite the relatively low influent carbon load, the B-stage P(D)N-S2EBPR system could achieve effective P removal performance, with the carbon supplement and redirection of the A-stage sludge fermentate to the S2EBPR. The novel process configuration design enabled a system shift in carbon flux and distribution for efficient EBPR, and provided unique selective factors for ecological niche partitioning among different key functionally relevant microorganisms including polyphosphate accumulating organisms (PAOs) and glycogen-accumulating organisms (GAOs). The combined nitrite from B-stage to S2EBPR and aerobic-anoxic conditions in our HRAS-P(D)N/A-S2EBPR system promoted DPAOs for simultaneous internal carbon-driven denitrification via nitrite and P removal. 16S rRNA gene-based oligotyping analysis revealed high phylogenetic microdiversity within the Accumulibacter population and discovered coexistence of certain oligotypes of Accumulibacter and Competibacter correlated with efficient P removal. Single-cell Raman micro-spectroscopy-based phenotypic profiling showed high phenotypic microdiversity in the active PAO community and the involvement of unidentified PAOs and internal carbon-accumulating organisms that potentially played an important role in system performance. This is the first pilot study to demonstrate that the P(D)N-S2EBPR system could achieve shortcut N removal and influent carbon-independent EBPR simultaneously, and the results provided insights into the effects of incorporating S2EBPR into A/B process on metabolic activities, microbial ecology, and resulted system performance.

Microaerophilic Activated Sludge System for Ammonia Retention toward Recovery from High-Strength Nitrogenous Wastewater: Performance and Microbial Communities

A transition to ammonia recovery from wastewater has started; however, a technology for sustainable nitrogen retention in the form of ammonia and organic carbon removal is still in development. This study validated a microaerophilic activated sludge (MAS) system to efficiently retain ammonia from high-strength nitrogenous wastewater. The MAS is based on conventional activated sludge (CAS) with aerobic and settling compartments. Low dissolved oxygen (DO) concentrations (<0.2 mg/L) and short solids retention times (SRTs) (<5 days) eliminated nitrifying bacteria. The two parallel MASs were successfully operated for 300 days and had ammonia retention of 101.7 ± 24.9% and organic carbon removal of 85.5 ± 8.9%. The MASs mitigated N2O emissions with an emission factor of <0.23%, much lower than the default value of CAS (1.6%). A short-term step-change test demonstrated that N2O indicated the initiation of nitrification and the completion of denitrification in the MAS. The parallel MASs had comparable microbial diversity, promoting organic carbon oxidation while inhibiting ammonia-oxidizing microorganisms (AOMs), as revealed by 16S rRNA gene amplicon sequencing, the quantitative polymerase chain reaction of functional genes, and fluorescence in situ hybridization of β-proteobacteria AOB. The microbial analyses also uncovered that filamentous bacteria were positively correlated with effluent turbidity. Together, controlling DO and SRT achieved organic carbon removal and successful ammonia retention, mainly by suppressing AOM activity. This process represents a new nitrogen management paradigm.