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Bioenergy Association of New Zealand (BANZ)Biogas from Municipal Organic Waste

Workshop 13 May 2010

Presentation by Humphrey Archer, Beca Infrastructure Ltd (humphrey.archer@beca.com) on

Digestate and Biosolids Utilisation

Presentation Overview

Definition of TermsOverseas Approaches to Digestate UtilisationNZ Guidelines for Biosolids UtilisationNZ examples of Digestate/Biosolids UtilisationChristchurch Overview of Organic Waste Processing

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Definition of Terms

In wastewater treatment, when sludge is stabilised (volatile fraction reduced) and “bugs” are reduced, sludge becomes biosolids. Stabilisation is typically by anaerobic or aerobic digestion, at elevated temperature. Biosolids was coined in 1991 by the Name Change Task Force of the Water Environment Federation (WEF). Other names considered were“humanure”, “urban biomass”, “organite” and “ROSE” (recycling of solids environmentally).Digestate is a general term covering the residual liquid and solids mixture after anaerobic digestion, used especially in biogas energy schemes.Solids can be removed from digestate using centrifuges or belt presses. The liquid stream is termed “separated liquor” and the solids “separated fibre”. The individual streams can be applied to land. Whole digestate (typically pumpable and <12% DM) can also be applied to land eg Invermay Energy Farm, Mosgiel in 1970’s/80’s.

Overseas Approaches to Digestate Utilisation

Focus of this presentation is mainly on production of additional biogas by digestion of waste organic material presently landfilled, composted or burnt (eg straw).Economics of biogas energy production will be dependent on efficient handling of digestate for reuse on land to gain the nutrient benefits. Otherwise, digestate disposal will be a significant cost.In UK, from early 2010, digestates can be approved under BSI PAS110, which is a specification sponsored by WRAP (Waste and Resources Action Programme) in conjunction with REA (Renewable Energy Association).With PAS110 approval, the digestate does not have to be registered as a “waste”, which has regulatory controls.Digestate is registered through the biofertiliser certification scheme, administered by Renewable Energy Assurance Ltd.BSI PAS110 was derived from other European examples.

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Structure of PAS110

Terms and DefinitionsQuality Management System (QMS)Hazard Analysis and Critical Contol Point (HACCP) SystemInput Materials allowedProcess ManagementMonitoring, Sampling and ValidationDispatch and Labelling

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Allowable Input Materials to Anaerobic Digestion (AD)

Biowaste – source-segregated waste of animal or plant origin which can be decomposed by micro-organisms, other larger soil-borne organisms or enzymesSource-segregated biodegradable materials eg catering wastesContaminated wastes not allowedSewage sludge is not “source-segregated”

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Insert table 1 from P31 (don’t include notes in red type)

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Annex A, table A1.1 (page 46) not red notes

Swedish Organic Waste to Biogas Plants

In 2007, there were 13 biogas plants producing 273,000 ton/year of digestate, which is applied to landIn 2006 about 18% of organic waste from households was treated in biogas or compost plantsNo organic waste for landfill and proposed to treat 35% organic waste by 2010Digestate certified through Swedish Waste Management Certification System. Wastewater sludges are not accepted under the certification system.Fibre fraction of digestate is regarded mainly as P fertiliser, and separated liquor as an N fertiliser

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NZ Guidelines for the Safe Application of Wastewater Biosolids to Land

Published by NZWWA and MfE in August 2003Contains list of parameters for monitoring of Biosolids similar to BSI PAS110Specific parameters not compared as yet – useful task to be doneNZ Biosolids Guidelines are based on USEPA and AU Guidelines. Generally considered as precautionary

NZ Examples of Wastewater Biosolids Application to Land

Estimated quantities from “in-tank” municipal wastewater plants is 55,000 tonnesDS per yearOnly three significant benefit reuse schemesNew Plymouth, raw sludge is dried to 92% DS in a Natural Gas fired rotary drum dryer. Dried granules are bagged as sold as Bioboost® to the public, golfcoursesand for ready lawn production.Nelson, Bells Island, aerobically digested (>500C) biosolids stream (at approx. 3% DS) is applied to forests on Plantation IslandChristchurch, anaerobically digested (mesophilic 350C) dewatered biosolidsspread on Burwood Landfill for surface restoration. In mid 2010, this will ceaseand new belt dryers will dry biosolids to 92% DS for reuse at coal mines.Sludge composting operations at Rotorua and Wellington have ceased – Rotoruadue to scarcity of wood chip for bulking and at Wellington, due to odour emissions and market limitations.These reuse schemes account for about 10% of the organic solids from WWTPs. Remainder is landfilled, so plenty of scope to increase application to land!

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Some Examples of Industrial Organic Waste Reuse

Fonterra Tirau, removes sludge from anaerobic lagoon annually and is applied mainly to maize cropping land. Lime is dosed to the anaerobic process for pH control and to remove Phosphorus, so sludge has high content of lime and P. SFF Belfast, on site DAF wastewater treatment process produces sludge which is dewatered and composted with wood and bark chip. Bio Blend® compost is sold to the public.

Enhanced Processing to Reduce Health Risks from Animal By-Products

From Annex A of BSI PAS110, to meet ABP Regulations, need either570C at 5 hours or 700C for 1 hour, plus 18 days storage. Similar to time/temperature requirements for sewage sludge. Thermophilic digestion at 550C to 570C typically has 3 to 5 days retention. Can operate in “feed, hold, spill” mode to reduce short circuit potential. Alternatively operate digesters in series.Thermophilic digestion increases the volatile solids destruction and biogas production typically by 15% and sometimes 30%.Batch heat treatment to 700C for 1 hour is also practised in Europe but not as widely adopted as thermophilic digestion.Further information on anaerobic digestion technologies is in a presentation by Archer to the 2008 BANZ Biogas Workshop in Hamilton.

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Christchurch – Overview of Organic Waste Processing

Christchurch collects food waste together with green waste which are composted in an enclosed tunnel system operated by Living Earth.Facility opened in March 2009.Compost and mulch products sold to the public.Wastewater Treatment Plant is being upgraded to handle predicted future growth and to allow beneficial reuse of the wastewater solids on land.Two new 7,000m3 thermophilic digesters are being commissioned at present, which will increase solids destruction and increase biogas production for use at the Plant and in Civic Facilities (refer to presentation in this workshop by Leonid Itskovich).Thermal Drying Facility nearing completion which will produce dried grannules at 92% DS. These will be used for coal mine restoration.

Christchurch Wastewater Treatment Plant

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80 tonnes per day of Dewatered Biosolids(after Anaerobic Digestion)

Economic / Environmental Drivers for Drying

land use change new regional landfill

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Community Drivers for Drying

Low GHG profileUses LFG resourceReduces leachate at landfillBest economics of suitable technologies.

Balance between energy productivity and cost effectiveness

Dried product is pathogen free and suitable for land rehabilitation and forestry fertiliser

Land application on non-food producing land on removal of contaminants

Drying provides a fuel productEnergy generation preferred disposal route subject to satisfactory air emissions

Fit with Recommended SolutionRecommendation from Consultation

Fuel for Drying

Winter conditions drive plant footprintVariability in energy quantity and availabilityLack of certainty in quality of process output

Free Environmentally friendly

Solar ( )

Particulate emission issuesSpecial handling plantAsh to landfill

Plentiful supply in NZRenewable sourceStable price over last 10 years

Wood ( )

Fossil fuel - high GHG emission profileExpensive imported fuel – price fluctuations

High energy valueClean fuel

Diesel/LPG (X)

Lower energy value than LPGPotential corrosion issuesReduce amount of electricity generation

Available on siteRenewable energy source – certainty of supply

Biogas ( )

Potential corrosion issuesTotal volume available uncertainLower energy value than LPG

Available near siteVery low costVery good GHG emission profilePotential for further carbon credits

Landfill gas ( )

DisadvantagesAdvantagesFuel type

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Drying Technology

Large footprintOdour emissions riskCommunity needs not met – not suited to land application, not suitable as fuelHigher GHG profile

Renewable energy (sunlight)Solar dryer (X)

DisadvantagesAdvantagesDryer type

Not well-suited to LFG or BiogasCannot use woodHigher safety risksHigh tech plant needs skilled operators and maintainers

Community needs met – fuel and/or land application on non-food areasProven in NZ (Hutt Valley and NP)Lower GHG profile (LFG)Grade “A” biosolids

Thermal drum dryer (X)

High tech plant needs skilled operators and maintainers.

Community needs met – fuel and/or land application on non-food areasWell suited to LFG and BiogasWell suited to woodLower GHG profile (LFG)

Thermal belt dryer ( )

Drying Vs Dewatered Sludge to Landfill

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Belt Dryer Process Schematic

Drying Plant Layout

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Energy Centre to left and Drying Plant to right

Drying Equipment with Hot Air Recycle Ducts