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!!

Thank you for your Attention!!Email and Website:

email: lmqueiroz@ufba.brwww.grse.ufba.br