Study and Proposed Pilot of Biogas Water Wash and Struvite Recovery Process at MMSD’s Wastewater Facilities Md Abul Bashar – Research Assistant, UWM (Presenter) Prof. Jin Li, Ph.D. – Principal Investigator, UWM Bryan Johnson, P.E. – Energy Tech Innovations, LLC

Study Outline Biogas Purification Phosphorus Recovery

Study Part 1: Biogas Purification

Methods of Biogas Purification Amine-Based Chemical Absorption (CHEM) Organic Solvent-Based Physical Absorption (PHY) Pressure Swing Adsorption (PSA) Water Wash (WW)

Why Water Wash? No additional chemical necessary Can remove problematic impurities with single simple step system. Both raw biogas and plentiful water is available at both of MMSD’s SSWWTP at JIWWTP. No corrosion in system instruments. Low energy consumption in treatment.

Objectives of Biogas Water Wash Study The Problem: Raw biogas can (be)  dirty  corrosive  have low BTU content  have higher cost to utilize for energy recovery purposes and flared because of it. Objectives: 1. Clean and purify biogas to remove H2S and Siloxanes using a lower cost process approach. 2. Upgrade 65% CH4 content in raw biogas up to 98%.

Biogas Water Wash ASPEN Plus Flow Diagram

Biogas Water Wash ASPEN Plus Modeling Results Absorber Pressure Water Flow (cfm) Biogas (cfm) Water Temp (F) Methane in PDRTGAS(%) Methane Loss (%) 45 psi 150 and 100 250 40 98.8 5.20 60 98 5.21 70 97.3 5.22 80 96.3 5.24 150 psi 38 and 25 98.7 2.94 97.6 2.98 96.6 3.01 95.3 3.10 Number of Absorbers: 2 Flash Pressure: 60 PSI

Biogas Water Wash ASPEN Plus Modeling Results Initial Methane Content = 65%

Significance and Innovation 30% Cost Savings Low operating Pressure (50 psi) Gas contaminant removal Less costly than natural gas Significance Non-metallic materials Unique internal Features Usable in both Parallel & Series Modular Scalable System Innovation

Study Part 2: Phosphorus Recovery

Phosphorus and Water Pollution Phosphorus discharge levels are creating significant environmental issues, algal blooms and GW drinking supplies. WWTPs and agricultural operations significantly contribute to this issue. Phosphorus discharge levels are becoming highly regulated and treatment is being increased. CO2 by-product may be integrated beneficially into phosphorus removal processes. Photo Source: MPR News

Phosphorus Content (as P2O5 ) Why Struvite? Chemical Formula of Struvite: (NH4)MgPO4•6(H2O) Phosphorus Content (as P2O5 ) Milorganite: 2.88% Struvite: 29% DAP: 46% Photo Source: The Home Depot and www.struvite.info

Pilot Scale Struvite Recovery Source: (AT Britton et al., 2007)

Struvite Solubility Product > Phosphorus is highly soluble in lower pH using recovered CO2 from biogas water wash separation process. > A pH of at least 8 for optimum phosphorus recovery can be integrated with CO2 removal, NaOH and MgCl2. Source: (AT Britton et al., 2007)

Completed Study will Summarize Correlate modeling to biogas water wash pilot performance demonstrating methane purification. Preliminary assessment of struvite recovery process in phosphorus removal. Study of both systems can be integrated to any waste water treatment plant with anaerobic digestion.

Thank you Questions?