Resource recovery and wastewater treatment technologies

The moderator of this session is: Luuk Rietveld (Professor of Drinking Water & Urban Water Cycle Technology)

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This session will include the speakers: Marinus J. Moerland (Department of Environmental Technology, Wageningen University and Research), Peter Cartwright, and Roos Goedhart (Water Management DepartmentDelft University of Technology)

Take a look at the abstracts below: 

Thermophilic and hyper-thermophilic anaerobic digestion as novel treatment technologies for safe nutrient recovery from concentrated black water 

Presenting author: Marinus J. Moerland

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Domestic wastewater, specifically its toilet fraction (black water; BW), contains nutrients (mainly nitrogen, phosphorous and potassium) that can be used as alternative fertilizer sources in the agricultural sector. During source separated sanitation different household waste streams are collected separately. The main fraction of nutrients and organic matter is present in BW. However also the main pathogen fraction ends up in BW, which restricts nutrient reuse. Within the Horizon2020 project Run4Life the challenge is to safely recover these nutrients through high rate thermophilic (55 °C) and hyper-thermophilic (70 °C) anaerobic digestion (TAD/HTAD) in Upflow Anaerobic Sludge Blanket (UASB) reactors. These innovative treatment technologies have the potential for simultaneous biogas production and pathogen elimination due to high temperatures to ensure safe reuse of recovered nutrients.  

Thermophilic and hyper-thermophilic anaerobic digestion (AD) are promising techniques for the treatment of concentrated black water. It was shown that thermophilic AD of concentrated BW reaches the same methanisation and COD removal as mesophilic anaerobic treatment of BW (conventional vacuum toilets) and kitchen waste while applying a higher loading rate (OLR) (2.5–4.0 kgCOD/m3/day) [1]. The retention time was 8.7 days with an organic loading rate of >3 kgCOD/m3/day. This resulted in a COD removal of 70% and a methanisation of 62% (based on CODt) during thermophilic AD. Hyper-thermophilic (70 ◦C) reached lower levels of methanisation (38%).  

During both TAD and HTAD  pathogen indicator organisms were removed to a high extent. Compared to mesophilic anaerobic digestion there is a significant increase in the removal of Escherichia coli and extended-spectrum β-lactamases producing E. coli. Both were almost fully eliminated during TAD and HTAD. Since there was no significant difference between TAD and HTAD in terms of pathogen removal, there is no additional benefit for hyper-thermophilic AD over thermophilic AD. Additionally, TAD has better COD removal and methanisation performance than HTAD. Therefore, TAD is suggested as novel treatment technology for concentrated BW with simultaneous pathogen removal. Next challenge is the development of efficient nutrient recovery strategies during TAD, preferably with separate product streams for nitrogen, phosphorous and potassium.  

Industrial Wastewater Recovery & Reuse: A case History

Presenting author: Peter Cartwright

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A large recreational facility in California is treating well water for all premise applications. It must meet the quality requirements of the USEPA Safe Drinking Water Act. The primary treatment technology was electrodialysis reversal (EDR), which generates wastewater during polarity reversal operations and electrode cleaning processes.

In an ongoing effort to conserve water supplies, the State of California strongly recommends the

practice of “zero liquid discharge” (ZLD). As this facility is committed to environmental sustainability, they had attempted to comply by recovering and reusing the wastewater from their EDR system, without success.

The facility employed a consultant who conducted extensive pilot testing to generate design data and effect the construction of a complete treatment system utilizing pressure-driven, crossflow membrane separation technologies to achieve ZLD. The design involves increasing the pH of the EDR wastewater with sodium hydroxide to effect precipitation of calcium, magnesium, and silica salts. The precipitate is concentrated in a tubular microfiltration (MF) system and further dewatered by a belt press with the solids removed to a landfill. Hydrochloric acid is used to lower the MF permeate pH and this stream treated by reverse osmosis (RO) to reduce the TDS to below 300 mg/L, and then directed to the potable water supply. The RO concentrate is pretreated by a crystallizer and fed to a falling film evaporator, followed by a centrifuge and hauled to a landfill. The distillate from these operations is also incorporated into the potable supply. The total volume of wastewater treated is 60,000 gpd (227 m³/day), and approximately 2600 lb/day (1183 kg/day) of solids are produced.

This presentation provides details of the chemistry, technologies utilized and description of the complete system design of this unique ZLD system.

Vivianite precipitation for iron recovery from anaerobic groundwater

Presenting author: Roos Goedhart

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Recovering of resources is common practice in wastewater treatment, but little applied to drinking water production. The conventional method for iron removal from groundwater via oxidation and filtration produces a large waste stream of aqueous sludge with little value. Backwashing the filter and treating the concentrated stream is the most cost-intensive step and reducing or reusing the iron sludge is recognized as one of the most important steps in increasing the sustainability of the industry. Groundwater use is expected to increase in the future and membrane technologies such as nanofiltration (NF) and reverse osmosis (RO) are becoming a competitive option to the conventional treatment technologies. The disposal of the concentrate, which contains high concentrations of iron, is a downside of these techniques and a proper treatment method should be found to deal with the stringent European legislation regarding disposal.

A novel method is proposed in which iron(II) is removed anaerobically from the water by precipitation as vivianite (Fe3(PO4)2 • 8 H2O) by dosing phosphate anaerobically to the water. Vivianite has an economical value and is used for the production of lithium ion batteries or as a slow P-release fertilizer.

The concept was tested in groundwater with natural iron concentrations of around 3.8 mg/L and a spiked solution of 100 mg Fe/L. The removal efficiencies, sludge volume and kinetics were compared to the method of iron oxidation. The formed precipitate was analysed by X-ray diffraction (XRD) analysis and the experiments were evaluated with the program Spec8 of the Geochemist’s Workbench® (GWB®) model to determine the saturation index (SI) of vivianite formation.

In iron-spiked groundwater, 93.7% was anaerobically removed, which increased to 99.9% after oxidation. Vivianite was the only solid phase detected by XRD and the volume of the sludge produced was a third compared to iron oxidation. With natural iron concentrations 16% was removed, the sludge volume was too little to measure. For both solutions removal stopped when the SI dropped below 4. To enhance further removal, the SI can be increased by increasing the pH. The model showed that the minimal iron concentration at which the SI is higher than 4, is 1 mg/L at a pH of 9.

A second order removal rate was found for the spiked groundwater with a rate constant of 2.27 M/s at a pH of 7. A half-time of 4 minutes was found for anaerobic precipitation, which is 4 times faster compared to iron oxidation.

Iron was successfully removed from groundwater via vivianite precipitation. This novel method has the potential to reduce the costs of drinking water production and can be a solution for the treatment of groundwater and of the anaerobic concentrate from NF or RO.

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