appendix 16 vermicomposting assessment - gisborne … · memorandum ch2m beca // 30 june 2017 //...

Appendix 16

Vermicomposting Assessment

CH2M Beca // 30 June 2017 // Page 1

6512659 // NZ1-14008069-13 0.13

Memorandum

To: Rachael Shaw Date: 30 June 2017

From: Julia van Eeden Our Ref: 6512659

Copy: Garry Macdonald

Subject: Gisborne WWTP Stage 2 Upgrade Memo 7 - Vermicomposting Assessment

1 Background

Gisborne District Council (GDC) is currently investigating options to provide tertiary treatment of

wastewater following discharge from the existing Biological Trickling Filter (BTF) at Gisborne

Wastewater Treatment Plant (WWTP). The existing domestic WWTP, which consists of inlet

screening, a BTF and an ocean outfall, was built and commissioned in December 2010, as the first

stage of a planned two-stage upgrade.

The original two upgrade options investigated in 2016 were:

� Option 1: Enhanced Wetland and Pond System (EWPS), based on process sizing and

operational inputs from NIWA; and

� Option 2: Conventional clarification, disinfection and biosolids handling and disposal;

During the Option Refinement phase, Council included a further option of installing a Biofiltro plant

after the existing BTF (at a remote site) to provide additional treatment prior to discharge to a

wetland. This utilises a combination of fixed film growth in wood chip media with a top layer of

worms.

All options produce biosolids streams in varying forms, which will require treatment and disposal

either as waste or as a beneficial product. Gisborne currently does not have a regional landfill.

Municipal solid wastes are transported to the Bay of Plenty for landfilling. There is a private landfill,

but under the terms of its operating consent it is not permitted to receive municipal wastes including

biosolids. Likewise, there is currently no established commercial composting or vermicomposting

operation within the region that could accept the biosolids from the WWTP. The operational costs

for both Option 1 and Option 2 (above) presented in the concept design report were based on

transporting dewatering biosolids (assumed to be in the range of 16 – 20% DS) out of district to

landfill, incurring significant on-going operational costs and providing no opportunity for beneficial

reuse.

At 16 to 20% DS the biosolids still contain a large quantity of water (80 to 84% water). Transport

costs are based on weight, and hence optimising the removal of water can significantly reduce the

transport costs.

One of the approaches to reduce transport costs and potentially achieve a product for beneficial

reuse is vermicomposting. This technology is complementary to GDC and the community’s desire to

favour natural processes over mechanically intensive systems where possible.

For the vermicomposting assessment, we have assumed two sludge options:

� Biosolid Option A: BTF sludge + conventional clarification (as per Option 2 of the Concept

Design Report)

� Biosolid Option B: BTF sludge + vermicast and wood substrate from Biofiltro process

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The biosolids from Option 1 in the Concept Design Report have not been assessed in this memo as

the full EWPS is unlikely to proceed. This memo provides a high level assessment and operating

cost and NPV assessment for vermicomposting of the Gisborne biosolids.

2 Design Basis

The system discussed in this document has been sized based on the sludge production rates from

the 2016 Option 2 concept design. It was assumed that this would be similar to the production rates

in other systems considered which include settling of BTF sludge. The proposed sludge

characteristics and volumes for vermicomposting are summarised in Table 1.

Table 1 – Potential Sludge Characteristic for Vermicomposting

Parameter Units Biosolid Option A Biosolid Option B

Upstream processes -

� BTF,

� Gravity settling

� Alum Dosing (optional)

� Sludge thickening and dewatering

� BTF

� Vermicast from Biofiltro process (combination of vermicast and wood substrate)

Solids concentration %DS 16-18% 10-15%

Volatile solids %VS 70-80% of DS 80% of DS

Dry solids mass

Peak

Average

kg/d

kg/d

3450

2540

With alum dosing:

3770

2860

-

2500 – 3500 T/year

‘Wet’ volume

Peak

Average

m³/d

m³/d

19-22

14-16

With alum dosing:

21 - 24

16-18

-

year

Notes: i. Solids from Biosolid Option A are based on a 5 d/wk operation.

ii. The solids from Biosolid Option B will be removed every 12-18 months and delivered to the facility.

Limited information is currently available on contaminant concentrations as the existing treatment

system does not produce a sludge stream. However there is some data available from a study of

the potential use of planted sludge treatment beds (PSTB) to treat and beneficially re-use settled

BTF sludge, which was undertaken between November 2014 and May 2017. During this trial,

sludge was collected and analysed for a suite of parameters in order to characterise the sludge in

terms of the chemical criteria specified in the NZ Biosolids Guidelines. The average trace metal

concentration values from this analysis are compared to the current guidelines for heavy metal

limits in Table 2. These values are assumed to be similar to what would be produced from settling

BTF sludge as the concentrations are based on dry matter mass fractions.

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Table 2– Comparison of Average Contaminant Concentrations with Guideline Limits

Parameter Trace Element Concentration (mg/kg dry weight)

Cd Cr Cu Pb Ni Zn

Average Concentration 0.35 13 37 15 16 263

Biosolids Limits – Grade a (2012 guidelines)

1 600 100 300 60 300

Biosolids Limits – Grade b (2012 guidelines)

10 1500 1250 300 135 1500

Proposed new Guidelines contaminant concentration limits

10 1500 1250 300 135 1500

Source: Horswell, J., Gutierrez-Gines, M.J., & Ambrose, V., Planted Sludge Treatment Bed Trial, Centre for

Integrated Biowaste Research, May 2017

The measured amounts of trace elements in the sludge are within the limits required to achieve

Grade a of the current New Zealand Biosolids Guidelines, which indicates they may be suitable for

application to land without any specific control measures. However there are a number of

contaminants listed in the Guidelines which were not tested in the study. Compliance with the limits

for these contaminants would need to be demonstrated before the sludge could be confirmed as

Grade a.

If the draft organic waste guidelines currently out for consultation are adopted, the sludge is likely to

meet these limits also as they are less stringent than the current heavy metal limits.

3 Vermicomposting System

3.1 Background

Vermicomposting is a simple biotechnological process of composting, in which worms enhance the

process of waste conversion. The worms breakdown the organic matter, such as sewage sludge,

and create an end product known as vermicast which has been shown to contain reduced levels of

contaminants and a higher saturation of nutrients. This process has commonly been applied in

home environments but recently is being applied on greater scales such as that shown in Figure 1.

It is one of the easiest methods to recycle waste which can then be applied to soil as a nutrient-rich

organic fertilizer.

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Open vermicomposting systems can generate odours, however these are reported to be minor and

earthy smelling. The system must be well ventilated to ensure gaseous oxygen gets to the worms

so there is proper decomposition.

The advantages of vermicomposting include:

� No capital cost for Council, as investment is by third party.

� Final product can be used to provide beneficial values back to the region

� Savings in transportation and disposal

� Low energy requirements

� Low maintenance requirements

Disadvantages include:

� Slow process

� Large land areas required

� May require a buyback of product (MyNoke)

� Potential stigma associated with biosolids limiting beneficial reuse by third parties

3.2 Composting in Gisborne

The Gisborne district has a strong focus on ‘zero waste’ within the region. They support the idea of

using sustainable approaches to process waste that is created within the community into something

that is returned with beneficial value. Currently there is a compost facility at D B Judd’s in

MacDonald Road that mixes bark with garden waste to produce a bagged garden product that is

exported out of town in commercial quantities.

The district also run a number of composting workshops and provide free composting bins (or a

small subsidy) for each rural household.

4 New Zealand Suppliers

There are currently two companies in New Zealand, Ecocast Limited and MyNoke, which have

established commercial scale vermicomposting facilities. Both of these suppliers were contacted on

the 13th March 2017 by CH2M Beca to provide the following information:

Figure 1 – Vermicomposting on a large scale

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� If any of the proposed options would not be suitable for vermicomposting

� If they could treat the biosolids at an existing facility or would need to build a new one

� Land area required for a new facility (including any recommended buffer zones – to be specified)

� Distance to the facility (existing or new)

� Proposed gate fee per wet tonne of sludge

� Any buyback requirements – percentage, the basis for the percentage and cost per tonne

� Bird management requirements.

This section compares the responses from the two suppliers. (http://doc.beca.net/NZ1/13754527)

4.1 Suitability for Vermicomposting

4.1.1 General Comments

Ecocast advised that the product from Option A is very suitable for vermicomposting when blended

with pine pulp/fibre. This would require 15 m3/day of fibre which would be transported to Gisborne

from Whakatane. They have not currently investigated local suppliers for fibre in the region. They

consider the product from Option B is best composted due to the presence of shavings from the

Biofiltro process.

MyNoke did not consider the Biofiltro biosolid product (Option B) to be suitable for vermicomposting.

They advised that the Option A biosolids would be suitable for vermicomposting subject to:

� Full analysis testing is provided enabling Noke Ltd to assess suitability

� Validation of mixing ratios with ‘other’ organic materials, achieved by a series of controlled trials.

Although it was not stated how much fibre would be required, MyNoke had previously engaged with

local industries and confirmed that they consider there to be sufficient fibre sources available in the

Poverty Bay region, however should it be required, a supplementary supply could be sourced from

Hawkes Bay.

4.1.2 Grading of the Final Product

Based the information in Table 2 MyNoke have further advised that:

� Based on the numbers supplied they expect that, with modifications to their mixing ratios and

availability of carbon based fibre from within the region, the sludge will return a compliant

vermicast under NZ standards.

� The co-blended product is expected to present no health / welfare issues for the composting

worms.

� Further pathogen reductions achieved during the conversion process will potentially provide an

Aa grade product.

� Consider there will be few issues with complying with any resource consent requirements

regarding ground water quality and odour.

� There may be some increase in metal concentrations, particularly high concentration metals

such as Zinc, due to volume reduction incurred during the conversion process. This is managed

through keeping clean fibre inputs at levels which keep the final product within the required

limits.

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4.2 Facilities

Ecocast has an established commercial facility in Tokoroa which treats municipal biosolids. They

have stated there is availability to process the biosolids and castings at their Kawerau site, however

suggest it makes more economical sense to establish the operation in Gisborne. It would cost less

to transport fibre to the processing site than to transport a higher volume of biosolids which also

comes with biohazard freighting issues.

MyNoke have facilities in Tokoroa, Maketu and Taupo which receive municipal Biosolids. They also

have a site dedicated to dairy manufacturing solids at Putararu. Whilst the municipal facilities could

accept the Gisborne biosolids material, MyNoke considered it would be more cost effective to

establish a facility in the Gisborne region and had already been engaging with industry and regional

end-users to confirm the potential viability of a Gisborne facility. In establishing a site they consider

the available space, proximity to dwellings and sensitive land areas, determination of surface, wood

substrate, land contour and storm water run-off and other areas of importance.

The site facilities required are relatively simple. The sites generally require the following

� A reception area for the incoming biomass and fibre.

� A mixing area where the biosolids are combined with the fibre to achieve optimum carbon to

nitrogen ratios. Mixing is achieved in purpose built vessels.

� The vermi composting area

� Stormwater and leachate would need to be managed within the site

4.3 Land Area Requirements

Ecocast has stated the land area requirement would be 10 hectares for either option, with a buffer

zone of 500 metres (prudent, but not essential).

MyNoke has a land area requirement of between 5 and 10 hectares subject to the type of land

provided.

4.4 Distance to Facilities

The distance from the Gisborne’s WWTP to the Ecocast processing facility in Kawerau is

approximately 220km.

MyNoke did not provide distances to any of their existing or proposed facilities.

Both vendors have supported the idea of a new vermicomposting system in the Bay of Plenty or

Gisborne region, due to the savings in transportation cost. It would be up to the supplier to

determine whether there is appropriate land to purchase or lease.

4.5 Proposed Gate Fees

Ecocast have proposed a cost of $70.00 per wet tonne for the product from Option A

(vermicomposting) and $85.00 per wet tonne for the product from Option B (composting).

MyNoke have stated they are unable to quantify a set rate prior to undertaking trials and selection of

a suitable processing site, however based on existing contracts they envision a budget of between

$48 and $74 per wet tonne of sludge.

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4.6 Buy Back Requirements

For facilities receiving municipal biosolids, MyNoke have incorporated a buyback arrangement in

order to limit their exposure to market resistance to use of the end product due to perceptions about

the use of a human derived biosolid. Notwithstanding the origin of the biosolid material, with the

correct ratio of fibre and nutrients, and maturation period, MyNoke advise that the vermicomposting

process can achieve Aa graded2 product. The buyback requirements are as follows:

� GDC to buyback of 75% of the completed vermicast product at a value of $25/tonne.

� A 70% volume reduction of the initial biosolid is achieved during the conversion process.

� The final product could be used by GDC on Council owned parks, gardens and other properties,

reducing the need for chemical fertilisers while also improving the environmental footprint.

Ecocast are not able to confirm whether they would able to sell either of the products due to the

biosolids component. Not factoring in any monetary recovery from sales, Ecocast are open to the

idea of giving the finished product back to GDC with the right to dispose of any surplus.

4.7 Bird Attraction

Ecocast have stated that neither vermicomposting nor composting processes attracts birds.

MyNoke has stated that bird attraction can be very location specific and are currently engaging with

local Fish and Game, DOC and other associated parties during their site planning process. Relating

to this topic, the VAR tends to be well managed by blending the biosolids with other suitable

material.

5 Cost Estimates

5.1 Options Considered

The cost estimates in this section have been prepared based on Option A only, as following

enquiries being issued to Vendors, Council decided not to pursue the Biofiltro process further.

5.2 Gate Fees

The cost of wood substrates and any capital costs to establish a facility is recovered through the

gate fee. As such there is no capital requirement from GDC. The gate fees from the two suppliers

were compared with the base case of disposing the biosolids to landfill out of district.

Table 3 – Gate Fee costs for various disposal methods per wet tonne of sludge

Base Case ($/yr) Ecocast ($/yr) MyNoke ($/yr)

$2201 70 48 – 74

Notes:

1. Includes cost of transportation. Contractor responsible for transporting waste to landfill includes the gate

fee in their charges

2 2003 NZ Biosolids Guidelines, soon to be superseded by the 2017 beneficial Use of Organic Waste Products

on Land

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5.3 Cost Analysis

The following assumptions were made to provide cost estimates of each option:

� Following conventional clarification and solids handling (i.e. clarifier, gravity belt thickener,

centrifuge) the annual biosolids production is assumed to be 630 t/yr on a dry basis

� The moisture content is assumed to be 16%DS

� The cost of substrates/fibre and any capital costs for the vermicomposting process are

recovered through the gate fee

� A transportation distance of 10 km has been allowed to a local vermicomposting facility

� Transporting biosolids to Ecocast’s Kawarau site was not considered viable due to the transport

costs being comparable to transporting to a landfill

� The cost of transporting and disposing of bought-back vermicast has not been included as the

disposal route for any bought-back vermicast has not been confirmed. We have assumed that

the product would be stockpiled on site for collection by GDC.

The following financial inputs have been used to calculate the cumulative cash flow prices of

processing the biosolids over a 20 year period:

Table 4 – Financial Inputs for Evaluating Whole of Life Cost of Processing Biosolids

Financial Inputs Value Source

Transport 2.7% CCC figures

Discount Factor 6.7% Previous report

Table 5 summarises the annual operating costs of processing the biosolids:

Table 5 – Annual Transport and Disposal Cost Estimates

Landfill Disposal (Base Case)

Ecocast MyNoke (range)

Transport and Gate Fee $866,000/yr $323,000/yr $236,000 - $339,000/yr

Buyback NA NA $52,000/yr

Total annual cost $866,000/yr $323,000/yr $288,000 - $390,000/yr

The 20 year whole of life cost for each of these options is shown in Figure 2.

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Figure 2 – 20y Whole of Life cost for each disposal method

6 Conclusion

If GDC proceeds with a WWTP option that produces a sludge stream, from the information above

vermicomposting appears to be a viable disposal route. However as the information from both

suppliers was preliminary in nature, and further work will be required to establish firm costs for this

option, in particular:

� Confirmed disposal fees and buy-back requirements

� Transport costs to a confirmed site

� Disposal route for any bought-back vermicast

Sarah Burgess

Senior Process Engineer Direct Dial: +64 4 896 9310+64 4 896 9310+64 4 896 9310 Email: [email protected]

appendix 16 vermicomposting assessment - gisborne … · memorandum ch2m beca // 30 june 2017 //...

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