Nutrient Recovery: A Focus on Ammonia

Transcription

1 Nutrient Recovery: A Focus on Ammonia January 17, 2014 Research Partnership Anaergia and MSU Relationship fostered through the installation of a 400kW anaerobic digester at MSU Anaergia looking to close the loop on several nutrient recovery equipment Dr. Dana Kirk, manager of the MSU Anaerobic Digester Research and Education Center Michael Theodoulou, Director of R&D for Anaergia MSU Anaerobic Digestion Research and Education Center A comprehensive centre for researching, developing and evaluating anaerobic digestion systems Facility includes labs, pilot facilities and multiple options for pilot scale systems Established streams for raw substrate, digestate, filtrate, cake and biogas Anaergia Global technology leader in the recovery of value from organic waste streams 20+ years of biogas experience Our core technologies are used in over 1,600 digester plants globally More than 355MW of global capacity installed

2 The Goal: Zero Organic Waste Future Wastewater Biosolids Source Separated Organics Renewable Power Renewable Gas Municipal Solid Waste Food Processing Waste Agricultural Waste Integrated Solutions Organic Fertilizer Clean Water Recovering Resources from Digestate Start with dilute nutrients in raw digestate (2% - 6% TS) 1) Use Solid-Liquid separation to isolate organic N & P in the cake 2) The liquid fraction will contain inorganic N & soluble K 3) Use ammonia stripping to recover ammonia-n from the filtrate either as liquid or pellet 4) The deammonified filtrate will contain organic N, P and largely K which can be concentrated and pelletized with cake Process Flow Diagram Biogas Food Waste Combined Heat and Power Unit Dewatering Electricity Manure Anaerobic Digestion Waste Heat Fertilizer Heat Exchanger Ammonia Stripping Acid Scrubbing Deammonified Dilution Water

3 Ammonia Stripping System Digestate from the AD process is separated using solid-liquid separation The liquid fraction (filtrate) is pre-heated using waste heat from CHP Heated filtrate enters first aerated tank-in-series where CO 2 is stripped which increases ph With ph >9.2 and temperature >140 F greater than 90% of ammonia can be stripped Subsequent tanks-in-series continue to strip ammonia until desired removal is achieved Ammonia rich gas from the strippers is sent to gas scrubbing (acid scrubber) Ammonia Ionization with Respect to ph and Temperature % Unionized NH F 122 F 131 F 140 F 149 F 158 F 176 F 194 F ph Importance of Solid-Liquid Separation Digestate from the AD will be rich in varying nutrients depending on the feedstock and high in TSS Suspended solids and fibres lower aeration efficiency and foul equipment S-L separation reduces potential precursors to high temperature/high ph precipitation In general, the phosphorous is bound with the organics and exits in the solid fraction Ammonia is fully soluble and remains in the liquid fraction

4 MSU Anaerobic Digester MSU Anaerobic Digester MSU Recipe 17 ton/d dairy manure 12 ton/d food and fruit waste 9 ton/d of fat, oil and grease (FOG) Feedstock High in Ammonia-N Food Waste

5 Feedstock High in Ammonia-N Manure Recipe for Success Digestate: 4,000 mg/l NH 3 -N 5,500 mg/l N 13,000 mg/l Bicarbonate Filtrate from UTS Screw Press Source of waste heat from combined heat and power unit (CHP) Knowledgeable staff and laboratory for analysis MSU Batch Scale Test of Stripping System Digestate from a full scale anaerobic digester treating a combination of food waste and dairy manure was screened using a filter screw press Filtrate was temporarily staged in a holding tank Ammonia stripping tank was filled in batch mode, heated using the hot water jacket and aerated Samples of the filtrate from the stripping tank was removed and examined during the batch testing

6 ph Relationship between ph and Alkalinity , , , , ,000 9 ph 8.8 4, Total Alkalinity 2, Time in Batch Reactor (min) Alkalinity (mg/l as CaCO3) 16 Relationship between ph and Alkalinity Anaerobic Digester gas has 60% CH 4 and 40% CO 2 High CO 2 levels results in higher aqueous CO 2 levels in the filtrate During air stripping, CO 2 is stripped which increases the ph and decreases alkalinity ph may be raised to between depending on digester feedstock and inorganic carbon concentration A slight dip in the ph as alkalinity removal flattens is the result of ammonia removal Percent Removal of NH 3 100% Ammonia Stripping 10,000 90% 9,000 80% 8,000 70% 7,000 60% 6,000 50% 5,000 40% 4,000 30% 3,000 20% 2,000 10% 1,000 0% Time (min) Actual Removal Model Removal Ammonia Concentration in Stripping Tank Concentration (mg/l as NH 3 -N) 18

7 Ammonia Stripping Air flow rate was found to be in range of / compare with 2,000 4,000 / in counter-current packed towers Aeration rate was found to be limited by liquid carryover into the gas overheads (think about shaking a bottle of pop and opening ) Carryover was eliminated by determining the maximum aeration rate and operating below said point During vigorous aeration, foaming was identified Mechanical foam suppression was used to control foaming Foam suppression should be handled case-by-case and may require use of anti-foaming agents (i.e., presence of surfactants, fats, oil and grease) What about Precipitation? Calcium phosphate and Struvite (magnesium ammonium phosphate) precipitate when ph 9 High turbulence/co 2 sparging conditions around diffusers are most susceptible to scaling After testing, tank inspection revealed no noticeable scaling Careful consideration must be made of the filtrate quality before aeration (i.e., soluble magnesium and orthophosphate concentrations) Ammonium Sulfate Production Liquid fertilizer with (N-P-K-S) or prilled into fertilizer pellet with Layer hen 7.6 lbs dry AMS/d per 1000 birds Dairy Cow 3.2 lbs dry AMS/d per lactating cow

8 Dilution Water Requirements Dry feedstock such as chicken manure, food waste and certain energy crops will require dilution to be treated through wet digestion processes Digesters may become toxic if excessive ammonia is loaded and therefore untreated filtrate might not be suitable as dilution water Ammonia content in digester should be <4,500 mg/l (NH 3 + NH 4 as N) with certain digesters operated at 6,000 mg/l (requires long time bacteria acclimation) Unionized ammonia fraction in solution (NH 3 -N) depends on temperature and ph - toxic to methanogens above 500 mg/l 40 TPD Chicken Litter Project 40 TPD Chicken Litter Project Scenario Large commercial egg farm in Singapore 490,000 laying hens 340,000 eggs per day Satisfies 8% of Singapore s egg consumption Activities produce 40 ton/d of manure from raised cage laying hens (expandable to 80 ton/d) No lagoons or allowable liquid discharge

9 40 TPD Chicken Litter Project 40 TPD Chicken Litter Project Solution Liquefy manure with filtrate & treat using AD 500 kw electricity kw heat using CHP Solid-liquid separation using a two stage screw press Filtrate treated using air stripping and ammonium sulfate production 3,800 lbs/d dry ammonium sulfate (800 lbs/d of nitrogen) equivalent Estimated $210,000/year in fertilizer value Additional 30 ton/d of 25% cake solids (N-P-K of ) Ammonia Stripping Layout