Composting as an alternative for final disposal of digestedsludge from UASB reactors: a case study in the smallmunicipalities of the state of Bahia, Brazil
Authors: Bárbara C. Lima, Laís M. Lima, Milena L. Brandão, Viviana M. Zanta, Daniele V. Vich, Luciano M. Queiroz
FEDERAL UNIVERSITY OF BAHIAPOLYTECHNIC SCHOOL
OVERVIEW
Bahia State:‐Located in the northeastern region of Brazil .‐ Total resident population of just over 15,2 million inhabitants distributed in 417municipalities.‐ The Human Development Index equals to 0.66.‐ 3/4 of the territory are in a semiarid region .
OVERVIEW
Rural Area of the Bahia State:‐158 municipalities have a population with less than 15,000 inhabitants.‐ The main economic activity in these small towns is the family agriculture .‐ Only 5% of these municipalities have some kind of wastewater treatment .‐ Septic tanks precariously constructed and without adequate maintenance expose the population to poor health conditions and cause notorious environmental degradation
Resource‐oriented sanitation and agro‐sanitation
OPPORTUNITY!!
OVERVIEW
Benefits Limitations
OBJECTIVES
The general objective was to investigate composting as an alternative for the valorization of digested sewage sludge from an UASB reactor
Test the use of woodchips as bulking agent and putrescible food waste as amendment agent
Perform a detailed physical‐chemical characterization of the compost quality
Verify the process financial aviability by the net present value (NPV) method
MATERIAL AND METHODS
Pile A Pile B
Pile C
Pile A - Phase 1 – Lasted 72 daysDay C (%) N (%) C:N OM (%)
1
34.8 3.0 11.4 74.2
Moisture (%) pH TotalColiforms E. coli
75.7 8.1 1.6x108 9.1x105
Pile B - Phase 1 – Lasted 72 daysDay C (%) N (%) C:N OM (%)
1
32.0 2.7 12.1 79.4
Moisture (%) pH TotalColiforms E. coli
73.2 7.9 2.8x108 3.4x105
Pile C - Phase 2 – Lasted 64 daysDay C (%) N (%) C:N OM (%)
73 (1)
28.1 4.1 6.9 75.2
Moisture (%) pH TotalColiforms E. Coli
56.4 5.4 >2.3x108 1.0x105
Characteristics of the piles at the beginning of the experiment
MATERIAL AND METHODS
Financial viability analysis - Net Present Value (NPV)
Rj = net cash inflow during the period tCj = total initial investment costsi = discount ratej = number of time periods
For the project to be financially viable, NPV must be greater than or equal to zero.
The discount rate adopted was that defined by the Special System for Settlement and Custody (Selic).
This system is managed by the Central Bank of Brazil and operated in partnership with Anbima, the Brazil’s Financial Market Entities Association.
RESULTS
Temperature during the composting process
0 10 20 30 40 50 60 70 80 90 100 110 120 130 14020
25
30
35
40
45
50
55
60Phase 2
Tem
pera
ture
(°C
)
Time (days)
Pile A Pile B Pile C Ambient
Phase 1
Criteria of the Brazilian legislation:-Class B: Temperature of 40°C for at least five days, with a peak occurring at 55°C over foursuccessive hours during this period.- Class A or Class B: Temperature should be kept above 40°C for at least 14 days and the averagetemperature during this period should be greater than 45°C.
RESULTS
(a) (b)
(c) (d)
(e) (f)
Time (days) Time (days)
0 10 20 30 40 50 60 70 80 90 100 110 12065
70
75
80
85Phase 2Phase 1
Org
anic
Mat
ter (
%)
Time (days)
Pile A Pile B Pile C
0 10 20 30 40 50 60 70 80 90 100 110 120275
300
325
350
375Phase 2Phase 1
Car
bon
(g.k
g-1)
Time (days)
Pile A Pile B Pile C
0 10 20 30 40 50 60 70 80 90 100 110 12020
25
30
35
40
45Phase 2Phase 1
Nitr
ogen
(g.k
g-1)
Time (days)
Pile A Pile B Pile C
0 10 20 30 40 50 60 70 80 90 100 110 1206
7
8
9
10
11
12
13Phase 2Phase 1
Car
bon/
Nitr
ogen
Time (days)
Pile A Pile B Pile C
Organic matter content; Carbon, Nitrogen and C:N ratio behavior during the experiment.
RESULTS
Parameter Brazilian Legislation Criteria Compost(Final of the 2nd phase)
Microbiological Aspects
Viable eggs of helminths(ovos per grams de TS)
< 0.25 (Class A) < 0.25 < 10 (Class B)
Thermotolerant coliforms(MPN per grams of TS)
<10³ (Class A) < 1.1 < 106 (Class B)
Parameter Brazilian Legislation Criteria Compost(Final of the 2nd phase)
Arsenic (mg.kg-1, dry weight) 41 <0.006Barium (mg.kg-1, dry weight) 1,300 -
Cadmium (mg.kg-1, dry weight) 39 2.4 ± 0.2Lead (mg.kg-1, dry weight) 300 <0.005
Copper (mg.kg-1, dry weight) 1,500 296 ± 24Chrome (mg.kg-1, dry weight) 1,000 18.8 ± 1.2Mercury (mg.kg-1, dry weight) 17 <0.0002
Molybdenum (mg.kg-1, dry weight) 50 23.7 ± 4.0Nickel (mg.kg-1, dry weight) 420 21.8 ± 3.2
Selenium (mg.kg-1, dry weight) 100 -Zinc (mg.kg-1, dry weight) 2,800 809 ± 28
Characteristics of the compost and limit required in Brazilian legislation
RESULTS
Physico-chemical analysis have high impact on
costs!!
Financial viability analysis - Net Present Value (NPV)
CONCLUSIONS
The main conclusions of the composting as an alternative to valorization of digestedanaerobic sludge from UASB reactors are :
It is necessary to add a rapidly biodegradable amendment agent so that the processreaches temperature in the thermophilic range. After addition of putrescible food waste,the compost pile reached temperatures above 55 ° C sustained for 6 days. The main aspect of the composting process as an alternative for final disposal andvalorization of digested sludge from UASB reactors in the small municipalities of the Bahiastate is to guarantee the occurrence of thermophilic temperatures and ensure thesanitization of the final compost.Local authorities who are responsible for health promotion and environmental qualitymust have a deep knowledge of the scenario of generation, management and treatment ofthose wastes through composting, in order to characterize the risk and define theinterventions and actions of governance and regulation.
There is no waste, There is Resources!!
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