Theory questions sum up to 16p and stand for 8/20

1. Why should we reuse water? Which microorganisms are present in water? Give their size range and how we could remove them. (2p)
2. How can we make microalgae cultivation more sustainable? (1p)
3. From which resources are Nitrogen, Potassium and Phosphorus fertilizer made of? Which of these is a critical raw material? What does a critical raw material mean exactly? (2p)
4. What is bio-oxidation? Explain this using the example of gold recovery. (1p)
5. What are the advantages and disadvantages of bioleaching compared to conventional chemical leaching? (0.5p)
6. What happens if the methanogenesis is inhibited during anaerobic digestion? (0.5p)
7. Name 3 key differences between anaerobic digestion and the carboxylate platform. (0.5p)
8. What is blackwater and what can be recovered from this? Explain how these categories are recovered from blackwater (and kitchen waste) at the Waterschoon project in Sneek. (1p)
9. Why is it bad if the aqueous film is too thick in compost (>65%)? (0.5p)
10. What are the different types of metal scarcity and give an example? (1p)
11. We want to precipitate Pd(II) via reducing it to Pd(0). The concentration of Pd is 3 mg/L, the molar mass is 106.42 g/mol. How much formate (NaHCOO) do we need to add? Molar mass of formate is 68.01. (0.5p)
12. What is the rate limiting step of anaerobic digestion? (0.5p)
13. Question out of the case study (1p)
14. Exercise: a CSTR with a volume of 50 m³ is used. The hydraulic retention time is 4 days. The concentration of organic mass of the wastewater is 45 g bCOD/L. What is the organic loading rate (g bCOD/L/d)? (4p) (answer: 11.25)

1) Why do we need water recovery? Give 4 problems with inorganics in water and how it can be measured.

Water recovery is essential for several reasons:

• Improving Water Supply Security: Reuse can enhance water availability for growing cities, industries, and agriculture by substituting potable water with recycled water for non-potable uses and augmenting potable supplies.
• Reducing Stress on Groundwater Aquifers and Surface Water Catchments: By reusing water, the demand on these natural sources is lessened, promoting their sustainability.
• Maintaining Environmental Flows and Wetlands: Reuse helps preserve vital ecosystems by maintaining the natural flow of water bodies and wetlands.
• Reducing Nutrient and Contaminant Load: Reusing treated wastewater reduces the discharge of harmful nutrients and contaminants into water bodies, protecting aquatic life and water quality.
• Addressing Environmental and Resource Scarcity Issues: The reuse of water helps in managing resources sustainably and addressing environmental challenges.
• Supporting Sustainable Resource Management and Circular Economy Practices: Water recovery is essential for sustainable resource management and promoting circular economy practices to address resource scarcity and environmental challenges.

The 4 problems with inorganics in water are:

• Heavy Metal Contamination: Heavy metals like copper, zinc, cadmium, and arsenic contaminate wastewater from metallurgical operations, posing threats to aquatic habitats.
• Acid Mine Drainage: This prevalent issue poses significant environmental risks, releasing acid and toxic compounds into water bodies.
• Sulphate Contamination: The mining and metallurgical industries produce substantial volumes of waste and process water contaminated with sulphate, contributing to global pollution.
• Sludge Characteristics: Sulphide precipitation, though costlier, offers better sludge characteristics compared to hydroxide precipitation, which is crucial for effective waste management.

The measurement of inorganics in water can be conducted through various methods, including:

• Adsorption: Using materials like activated carbon to measure the efficiency of removing heavy metals from water.
• Chemical Precipitation: Forming insoluble precipitates that can be separated from water, allowing for the measurement of metal recovery.
• Ion Exchange and Membrane Filtration: These methods are explored for their effectiveness in removing heavy metals and other inorganics from water.
• Biosorption and Bioreduction: Using microbial or algal biomass to measure the removal efficiency of heavy metals and other inorganics.

2) Bioleaching vs bio-oxidation + example. Direct reduction vs indirect reduction + examples

Bioleaching is a process that utilizes microorganisms to extract metals from low-grade ores by converting metal sulfides into soluble metal sulfates through microbial oxidation of iron and sulfur compounds. An example is the Talvivaara mine in Finland, where metals such as nickel, cobalt, copper, and zinc are extracted through a process that includes open-pit mining, crushing, heap bioleaching, and metal recovery.

Bio-oxidation involves the microbial oxidation of sulfide minerals to expose the metal content, making it more amenable to subsequent chemical extraction processes. It is often used as a pretreatment step to enhance the recovery of metals like gold from refractory ores.

3) Why is photosynthesis limited at high light inputs

Photosynthesis is limited at high light inputs because excessive light can lead to photo-saturation and photo-inhibition, which damages algal cells due to the production of reactive oxygen species.

4) Sulfur cycle in a sewer: give reactions + what group (not species) of organisms?

• Sulfate Reduction: Under anaerobic conditions, sulfate (SO₄²⁻) is biologically reduced to sulfide (HS⁻). Reaction: SO₄²⁻ + organic matter → HS⁻ + H₂O + CO₂
• Formation of Hydrogen Sulfide: Sulfide can form hydrogen sulfide (H₂S) through reactions common in sewer systems with high organic matter and anaerobic conditions. Reaction: HS⁻ + H⁺ → H₂S
• Oxidation of Hydrogen Sulfide: In partially full sewers, H₂S escapes from the liquid phase and can be oxidized by sulfur-oxidizing bacteria to sulfuric acid (H₂SO₄). Reaction: H₂S + 2 O₂ → H₂SO₄

Groups of organisms are sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria. SRB operate in strict anoxic conditions where sulfate is the final electron acceptor and multiple electron donors are possible. Sulfur-oxidizing bacteria oxidize hydrogen sulfide (H₂S) to sulfuric acid (H₂SO₄).

5) UASB vs CSTR? What operational conditions for both?

Upflow Anaerobic Sludge Bed (UASB):

• Solid-Liquid Separation: Contains solid-liquid separation of the effluent and return of the solids.
• Volumetric Loading Rates: High volumetric loading rates with an Organic Loading Rate (OLR) between 15 and 20 kg COD/m³/d.
• Hydraulic Retention Time (HRT) vs. Solids Retention Time (SRT): HRT is much shorter than SRT.
• Upflow Velocity: Approximately 1 m/h to avoid sludge wash-out.
• Application: Suitable for low to medium strength wastewaters, commonly applied in the brewery and dairy industry.
• Zones: Two main zones in the reactor: the settling zone (for settling of sludge dragged up by biogas) and the sludge zone (concentrated sludge bed).

Continuous Stirred Tank Reactor (CSTR):

• Solid-Liquid Separation: Normally operates without biomass recirculation.
• Mixing: Mixing is crucial; insufficient mixing leads to poor COD degradation, while excessive mixing can disturb syntrophic interactions and cause foam formation.
• Organic Loading Rate (OLR): Moderate OLR of 3-10 kg COD/m³/d.
• Hydraulic Retention Time (HRT) vs. Solids Retention Time (SRT): SRT equals HRT, which ranges from more than 20 days up to 150 days.
• Application: Used for waste streams such as waste-activated sludge, manure, organic fraction of municipal solid waste (OFMSW), and energy crops.

6) Physicochemical processes in first week of composting?

During the first week of composting, the following physicochemical processes occur:

• Temperature Rise: There is a typical temperature rise in windrow compost turned mechanically. High temperatures cause rapid conversion rates (40-50°C) and hygienization.
• Oxygen Consumption: Oxygen present in the air moves through the composting mass, which is crucial for aerobic decomposition.
• Moisture Content: The ideal moisture content is between 40-65%. If the moisture content is less than 40%, microbial activity slows down, and if it is more than 65%, water displaces much air in the pore space of composting materials.
• Carbon to Nitrogen (C/N) Ratio: The C/N ratio is adjusted by mixing different types of organic materials to optimize the composting process.

These processes are essential for the initial breakdown of organic matter and setting the stage for further decomposition and stabilization.

7) Why is the nutrient cycle out of balance + consequences?

The nutrient cycle is out of balance primarily due to the industrialization of processes like the Haber-Bosch process, which captures nitrogen (N₂) and converts it to ammonia (NH₃). This process consumes 0.75% of global energy and 3.3% of natural gas consumption. As a result, reactive forms of nitrogen are accumulating in environmental reservoirs. One significant consequence of this imbalance is the rapid increase in ocean 'dead zones' over the last 60 years, doubling each decade. These 'dead zones' have been reported in more than 400 systems, affecting an area of 245,000 km².

8) What is black water, why vacuum system?

Black water (BW) refers to brown faeces and toilet paper, which are involved in energy (biogas) production and flow under gravity. The amount of water affects transport (clogging) and energy production. Vacuuming the system is beneficial because it reduces water use, which is crucial for the efficient operation of the system.

9) Exercise: (metabolism scheme given) if we have 40 g/L glucose, how many g/L acetate do we get?

10) Waste stream with Na₂SeO₄, we want to reduce this to remove the Se, with glucose. To what oxidation state does Se have to go? 100 m³/h waste stream, conc of Na₂SeO₄ is 5 mg/L

2 Questions about the students' presentation.

Vraag 1

motivations for water reuse

Reusing water is crucial for sustainable water management. It helps address environmental and resource scarcity issues by ensuring water quality through various technologies like membrane filtration and disinfection. Additionally, water reuse can aid in the removal of micropollutants and inorganic chemicals, making it a vital component of sustainable resource management and circular economy practices. This approach not only conserves water but also supports nutrient recovery and biofuel production, contributing to overall sustainability and innovation in wastewater treatment processes.

micropollutants in water

Micropollutants present in water include pharmaceutical and personal care products (PPCP), endocrine disrupting chemicals (EDC), and disinfection byproducts (DBP).

Vraag 2: rekenoefening over sulfaat

Vraag 3

vergelijk CSTR, UASB, AnMBR

Continuous Stirred Tank Reactor (CSTR)

• Flow Direction: Upflow.
• Organic Loading Rate (OLR): 3-10 kg COD/m³/d.
• Mixing: Mixing is crucial; different systems exist for mixing, including mechanical mixing, sludge recirculation (limited), or biogas recirculation (foaming).
• Solids Retention Time (SRT) and Hydraulic Retention Time (HRT): SRT = HRT > 20 days up to 150 days.
• Applications: Used for waste-activated sludge, manure, OFMSW, and energy crops.
• Advantages: Simple system, normally without biomass recirculation.
• Disadvantages: If mixing is too low, there is insufficient COD degradation; if too high, there is a disturbance of syntrophic interactions and foam formation.

Upflow Anaerobic Sludge Bed (UASB)

• Flow Direction: Upflow.
• Organic Loading Rate (OLR): 15-20 kg COD/m³/d.
• Upflow Velocity: 1 m/h to avoid sludge wash-out.
• Zones: Two main zones: settling zone (settling of sludge dragged up by biogas) and sludge zone (concentrated sludge bed).
• Applications: Suitable for low to medium strength wastewaters; applied in the brewery and dairy industry.
• Advantages: High volumetric loading rates, good for low to medium strength wastewaters.
• Disadvantages: High salt leads to granule disintegration.

Anaerobic Membrane Bioreactor (AnMBR)

• Flow Direction: Downflow.
• Organic Loading Rate (OLR): Up to 25 kg COD/m³/d.
• Separation: Contains solid-liquid separation of the effluent and return of the solids.
• Combination: Combines anaerobic biological treatment and membrane separation.
• Mixing: High mixing intensities are possible, but this consumes energy and may disturb syntrophic interactions.
• Advantages: Increased COD removal efficiency, improved biogas production, reduced system footprint.
• Disadvantages: Membrane fouling, requiring regular cleaning.

CSTR is a simple system with moderate OLR and crucial mixing requirements, suitable for various waste streams but sensitive to mixing intensity. UASB has a higher OLR and is effective for low to medium strength wastewaters, with specific zones for sludge management but is sensitive to high salt concentrations. AnMBR offers high OLR and combines biological treatment with membrane separation, providing high efficiency and biogas production but requires regular maintenance due to membrane fouling.

Waterschoonproject: geef de 2 belangrijkste resource recoveries

Verklaar fotolimitation, fotosaturation, fotoinhibition

Photolimitation, photosaturation, and photoinhibition are terms related to the efficiency of photosynthesis in microalgae, which depends heavily on the quality and quantity of light.

• Photolimitation: This occurs when the light intensity is too low to support optimal photosynthetic activity. In this state, the rate of photosynthesis is limited by the availability of light.
• Photosaturation: This happens when the light intensity reaches a level where increasing it further does not result in a higher rate of photosynthesis. The photosynthetic apparatus is operating at its maximum capacity.
• Photoinhibition: This occurs when the light intensity is excessively high, leading to damage to the algal cells due to the production of reactive oxygen species. This results in a decrease in the rate of photosynthesis.

Waarom Fe in mineraal aanwezig bij bioleaching

Fe is present in the mineral in the bioleaching process because chemolithotrophic bacteria like Thiobacillus species oxidize ferrous iron or sulfur compounds, producing sulfuric acid that facilitates metal solubilization.

Teken MFC

Vanwaar komen de N en P nutriënten

The sources of nitrogen (N) and phosphorus (P) nutrients include:

• Nitrogen: Nitrogen can be sourced from ammonium (NH₄⁺) and nitrate (NO₃⁻). Bio-based N fertilizers, which tend to contain a higher amount of mineral N in NH₄⁺ form, are also a source of nitrogen.
• Phosphorus: Phosphorus is taken up as inorganic phosphate. Phosphate rock is a significant source of phosphorus, with 90% of mined phosphate rock used as fertilizer.