evaluation of a trickle flow leach bed reactor for anaerobic digestion of high solids cattle waste

EVALUATION OF A ‘TRICKLE FLOW LEACH BED REACTOR’ FOR ANAEROBIC DIGESTION OF HIGH SOLIDS CATTLE

MANURE

Authors: Asma Hanif – Graduate Research Student, Colorado State University

Lucas Loetscher, Graduate Research Assistant, Colorado State University

Sybil Sharvelle - Assistant Professor, Colorado State University

Kelly Wasserbach – Graduate Research Assistant, Colorado State University

Introduction

Colorado – Second highest producer of cattle manure in the United States (19 million tons of manure/yr)

Difficulties in organic solid waste management

Growing demands for renewable sources of energy

Anaerobic digestion of the produced cattle manure - Biomass energy equivalent to 46 billion BTU/day

BackgroundOperational anaerobic digesters in the US as of September 2012 (Source: EPA)

Anaerobic digestion in Colorado

Second highest producer of cattle manure in the US yet

no operational digesters

Reasons:

o Arid climate - Produced cattle manure is very dry (approximately

90% total solids)

o Limited water resources

Types of anaerobic digesters

Leach Bed Reactors (LBRs)Advantages:

• High solids reactor

• Low water requirements

• Low energy requirements

• Good methane yields

Limitations:

• Reactor clogging leading to lower

hydrolysis efficiency

• Prolonged start-up time

• VFA accumulation over time

Proposed System Design Multi-Stage Leach Bed Reactor (MSLBR) System

TFLBR – Trickle flow leach bed reactorHRAD – High rate anaerobic digester

Overview• Cattle Manure – Collection & Preparation

• Loading Reactors

Manure in TFLBR

Wooden Block

Metal Pole

Sleeve

Weight

Analytical Results

Total Solids (TS), Volatile Solids (VS) & Fixed Solids (FS)

• Approximately 23% of cattle

manure is hydrolyzed in the

TFLBRs

• The average VS reductions

(in terms of TS) was 71.8%

Chemical Oxygen Demand (COD)

The TFLBRs undergo approximately

66.32% of COD reduction due to COD

leaching during hydrolysis.

Approximately 44% of the total COD is

leached out of the TFLBRs over the period

of six weeks.

Biochemical Methane Potential (BCMP) Test

BCMP tests validate that leachate collected from the TFLBRs have a CH4 potential of 0.43 L CH4/g COD

Conclusions• Proposed MSLBR system is the best technology fit for

digesting high solids cattle manure produced in CO.

• High biogas yields from BCMP tests indicate the successful hydrolysis of the cattle manure using TFLBRs

• Pilot scale studies monitoring the VFA concentrations under leachate recirculation would provide a better understanding of the MSLBR system

Thank You

History of LBRs• LBRs with ‘Municipal Solid Wastes’ (MSWs)

• Initial waste saturation to improve leaching potential• Inert bulking agents to avoid clogging due high density wastes• Comparison between upflow and downflow leaching • Sequencing between a batch of fresh and stabilized waste bed

• LBRs with ‘Lignocellulosic Biomass’ (LB)• Leachate recirculation to improve system yield• Hydraulic flush – to control pH/VFA concentration inside the LBR

• LBRs with Cattle manure • Co-digestion • Trickling inoculum

(All the above discussed LBRs handled OSWs not more than 26% TS)

Objectives

• To design an LBR capable of handling the high solids cattle manure produced in Colorado

• To evaluate the organic leaching potential of the designed LBR to

check the extent of successful hydrolysis

• To optimize the operation of the designed LBR to achieve maximum

hydrolysis efficiency in a single pass system

Evaluation of a TFLBR operation without leachate recirculation

Three phases of reactor experiments were conducted to

study and optimize TFLBR operation

• Reactor Experiments – Phase I

• Failure of hydrolysis due to clogging

• Reactor Experiments – Phase II

• Addition of straw as a bulking material

• Addition of a layer of dispersion media

• Reactor Experiments – Phase III

• Addition of nutrients to improve bacterial activity

Overview• Cattle Manure – Collection & Preparation

• Pulverization • Sorting

• System Construction & Setup• Loading Reactors• System Operation & Sampling• Analytical Tests

• Total Solids (TS), Total Suspended Solids (TSS), Total Dissolved Solids (TDS), Volatile Solids (VS), Fixed Solids (FS), Chemical Oxygen Demand (COD), Total Nitrogen (TN), Total Phosphorus (TP), Total Potassium (TK) and Total Volatile Fatty Acids (TVFAs)

• Biochemical Methane Potential (BCMP) tests

Reactor Experiment – Phase I

• Three TFLBRs (triplicate) loaded with high solids CW

• Water inflow rate 20 mL/min

• System failure within the first 24 hours

- Water build-up on top of the waste bed due to clogging

Reactor Experiment – Phase II• Addition of straw as a

bulking material (5% by mass)

• Comparison between TFLBRs containing CW bulked with and without straw

• Layer of fine sand on top of waste bed to promote water dispersion through the column

Reactor Experiment – Phase III• Addition of nutrients to

check if the TFLBR is nutrient limited due to continuous leaching without recirculation

• Comparison between nutrient dosed and non-nutrient dosed TFLBRs

• Composite sampling technique instead of instantaneous sampling

Comparison between Phase I, II & III

0 2 4 6 8 10 12 14 16 18 20 22 240

5

10

15

20

25

30

35

40

45

50

Phase II - Without Straw Phase II - With Straw

Phase III - Without Nutrient Dosing Phase III - With Nutrient Dosing

Time (Days)

g C

OD

/ L

leac

hat

e

Biochemical Methane Potential Test