Production of Biofertilizer from Vermicomposting Process of Municipal Sewage Sludge
Z. Siti Zahirah,
This study examines the potential of tiger worms (Eisenia fetida) in vermiculturing Municipal Sewage Sludge (MSS) into beneficial vermicompost or biofertiliser. Tiger worms weighed 1000 g were cultured in plastic bin (45x30x30 cm) containing 25000 g sewage sludge taken from a selected sewage treatment plant in Malaysia. The daily feeding rate of MSS was made to be equal with the weight of worm biomass. Sludge volume reduction due to vermicomposting process was determined daily. Physical parameters such as temperature, moisture content and pH were recorded. Nutrient contents in vermicompost such as Total Nitrogen (TN), Total Phosphorus (TP) and Total Potassium (TK) were determined for day 1, 7, 14 and day 21. Results showed that vermicomposts produced by tiger worms gradually possessing higher nutrient contents as the composting process progressed. Total nitrogen was found to increase from 19.6 to 35.7 mg L-1, total phosphorus from 9.45 to 10.87 mg L-1 and total potassium from 3.44 to 4.80 mg L-1, respectively. In addition conversion of MSS to vermicompost was found to be 93% by weight and worm biomass showed 30% increment from its initial weight within 21 days. Thus, the present study showed vermicomposting of MSS into organic fertiliser is feasible besides providing a safe and practical disposal method for sewage sludge.
Process of sludge disposal from the residual of wastewater treatment plants
can pose a serious environmental problem thus stricter environmental regulations
need to be imposed. In conjunction, the awareness of environmental problems
has forced governments, local authorities and utilities for management to search
for new alternative processes or solutions for future waste management strategies
(Solisio et al., 2002; Moreno
et al., 2009; Bayat and Sari, 2010; Yadav
et al., 2010). Effective solid and liquid separation persists to
be a major problem in various operation units in waste- water treatment. Among
them, sludge dewatering has been pointed out as one of the most expensive and
least understood processes. Biosolids are the nutrient rich by-product of wastewater
treatment, generated by channeling human waste through treatment plants and
collection systems. Although, the terms biosolids and sewage sludge are often
used interchangeably, biosolids are the end product after treating sewage sludge
with anaerobic digestion in combination with heat (Decaens
et al., 1999; Elissen et al., 2010).
The use of biosolids as soil amendments (soil conditioners or fertilizers) or
for land reclamation has reduced the volume of biosolids that must be landfilled,
incinerated, or disposed of at surface sites. In the last several years, numerous
scientific, political and social factors have contributed to a growing public
concern over the safety of biosolids which has resulted in strict local ordinances
banning. Therefore, the concept of organic matter recovery is becoming more
popular to be applied for various purposes. Composting as a resource recovery
is becoming a more acceptable alternative for sludge treatment due to potential
use for land application as bio fertilizer and soil conditioner (Gupta
et al., 2005; Suthar et al., 2008;
Niwagaba et al., 2009). The organic portion of
solid waste however could be utilized in a very profitable way by composting
or by using vermicomposting process (Mainoo et al.,
2009; Singh et al., 2010; Ganesh
et al., 2009). Vermes is Latin word for worms and vermicomposting
is essentially organic composting with worms. In general vermicomposting aids
in the disposal by improving the physical quantities of waste (Khwairakpam
and Bhargava, 2009; Yadav and Garg, 2009). The use
of earthworm in sludge management has been termed as vermistabilization.
Vermistablization represents a technology that is environmentally sound and
relatively new technology that can be classified as an innovative and alternative
technology (Follet et al., 1981; Hand
et al., 1988; Surindra, 2009). Earthworms
have been used for waste stabilization for many years, especially in Southeast
Asia and some third world countries mainly, Canada, United States, Australia
and France. Earthworms are one of the major soil macro invertebrates and are
known for their contributions to soil formation and turnover with their widespread
global distribution. In particular, most of the sewage sludge related to vermicomposting
studies employed, activated sludge (a product of biological wastewater treatment)
as the raw substrate, however there is a paucity of data on the possibility
of vermicomposting the primary sewage sludge which is available in huge quantities
(Madan et al., 1988; Singh
and Sharma, 2002). Thus in the present study, an investigations have been
established on the viability of using earthworms as a treatment technique for
a selected Malaysians municipal sewage sludge besides producing beneficial
MATERIALS AND METHODS
Earthworm collection: Composting species of tiger worms (E. fetida) were chosen as the vermicomposter. Earthworms of E. fetida was bought from the earthworm farm at Kuantan, Pahang of Malaysia. About 1000 g of tiger worms were used in this study. Sewage vermicomposting process was done from 18 August 2009 till 9 September 2009.
Municipal Sewage Sludge (MSS): Sewage sludge was taken from sewage treatment plant at Indera Mahkota Kuantan, Pahang Malaysia. In this study, 25 kg of dry sewage sludge was used as a feeding substance for the earthworms within 21 days vermicomposting period.
Experimental set up: The sewage sludge was introduced in the vermibin without any pretreatment. The average
cumulative moisture content of MSS as collected from the site was 60-70% (wet basis). The initial temperature of the sludge was measured as about (27-29)°C and it remained constant for a couple of days. Vermibin by the dimension of 1x0.5x0.5 m (Fig. 1) was used to study the organic degradation of sewage sludge by the earthworm. Therefore a total of 25 kg sewage sludge was fed to the worms. Temperature and moisture content were maintained and the data was recorded thrice a week as shown in Table 1.
On the other hand, the characterization of treated sewage sludge was done before and after it was fed to the worms. Sampling was made every 7 days until day 21 of composting period. Sludge characterization includes physical parameter of pH and chemical properties of Total Nitrogen (TN), Total Phosphorus (TP) and Total Potassium (TK). Besides that the actual mass reduction of sewage sludge during vermicomposting was also recorded.
Vermicast analysis: On each day of 1, 7, 14 and 21, vermicast sample was collected and sieved. The vermicast was sieved with hand sorter (net mesh or gauge wire) in order to separate the earthworm and vermicast before its weight was taken. Then, 1 g sample (vermicast) was added into 1 L distilled water for laboratory analyses works. Each dried vermicast sample was analyzed for the following parameters: pH (using standard method, pH meter), total Nitrogen (TN) using hach method (DR2500, method10071), Total Phosphorus (TP) using hach method (DR2500, method8049) and Total Potassium (TK) using a hach method (DR2500, method 8190).
measured range of parameters
design of vermibin
RESULTS AND DISCUSSION
Total Nitrogen (TN): The application of 1 kg earthworm to 25 kg sewage
sludge has significantly changed its physical structure and chemical composition
whereby the total nitrogen content has been found to increase by 82%. As shown
in Table 2, the total nitrogen has increased from 19.6 to
35.7 mg L-1 within 21 days of vermicomposting. This result apparently
showed that vermicomposting process affects mineralization of nitrogenous organic
compounds and the amount of sewage sludges nitrogen content, thus suggesting
that sewage vermicomposting is eminently viable in treating the sewage sludge
besides enriching its beneficial nitrogen composition. In particular, the earthworm
activity enriches the nitrogen profile of vermicast through microbial mediated
nitrogen transformation and addition of mucus and nitrogenous wastes secreted
by earthworms. On the other hand, Ruz-Jerez et al.
(1992) claimed that such condition was attributed to the increased in oxidized
carbon due to soil ingestion and not to changes in the soil texture.
Besides releasing N from compost material, earthworms also enhance nitrogen
levels by adding their excretory products, mucus, body fluid and enzymes to
the substrate. Suthar et al. (2008) suggested
that the decaying tissues of dead worms also add a significant amount of N to
vermicomposting sub-system. In particular the nitrogen enrichment pattern and
mineralization activities mainly depend upon the total amount of N in the initial
waste material and on the earthworm activity in the waste decomposition sub-system.
pH: Changes in pH value during vermicomposting process are shown in
Table 2. Vermicasts pH was found to decrease from 6.3
to 5.4 after 21 days. This result showed that vermicomposting produces acidic
compound by-product that could be due to microbial decomposition during vermicomposting.
In fact this statement is consistent with Elvira et al.
(1998), who suggested that production of CO2 and organic acids
by microbial decomposition during vermicomposting was the underlying factor
for the pH decrement.
data obtained from vermicomposting process
Total Phosphorus (TP): As shown in Table 2 vermicomposting
has increased the vermicasts phosphorus content up to 14% during the three
weeks time. This result apparently showed that vermicomposting can supply biodegradable
phosphorus for plantation instead of chemically synthesized phosphorus sources.
Similarly, Ghosh et al. (1999) have reported
that vermicomposting can be an efficient technology for the transformation of
unavailable forms of phosphorus to easily available forms for plants. It is
hypothesized that vermicomposting process releases TP content from organic waste
due to the activity of earthworms phosphatases. In addition further release
of TP is attributed to the phosphorus solubilizing microorganisms that is present
in the worm casts (Ghosh et al., 1999; Elvira
et al., 1998). In similar statement, Lee (1985)
claimed if the organic materials pass through the gut of earthworms, then some
of phosphorus being converted to such forms that are available to plants. He
further concluded that the availability of TP to plants is mediated by phosphatase
produced within the earthworms and further release of TP may be introduced by
microorganisms in their casts, after their excretion.
Total Potassium (TK): Total potassium content of sewage sludges
vermicast by the end of vermicomposting process is shown in Table
2. An increased in Total Potassium (TK) was recorded in the vermicast than
the initial feed mixtures. Total potassium content of vermicast was gradually
increased (up to 38%) within the 21 days period. Consistently, our data is supported
by Orozco et al. (1996), who reported an increased
in TK in coffee pulp and textile mill sludge during vermicomposting. This increased
maybe due to the microbes present in the gut of earthworms which might have
played an important role in this process, in fact Premuzic
et al. (1998) claimed acid production by the microorganisms is the
major mechanism for solubilizing insoluble potassium in the organic waste.
The final weight of tiger worms was found to be higher by the end of vermicomposting
period. As recorded in the Table 3, the worms weight
has increased by 38% from its initial reading. This finding is consistent with
Contreras-Ramos et al. (2005) whereby their study
showed that earthworms increased their weight by 35% when soil was amended with
5% sewage sludge in spite of contamination with hydrocarbons but lost 77% weight
without sewage sludge after 70 days.
rate of earthworms in vermibin
They concluded that if the weight-increased of worms is accounted for, the
nutrient content of ingested organic material largely makes up for the nutrient
content of incorporated in the soil. Besides that, Suthar
et al. (2008) summarized that the factors relating to the growth
of earthworms may also be considered in terms of physiochemical and nutrient
characteristics of waste feed stocks. Thus, organic waste palatability for earthworms
is directly related to the chemical nature of the organic waste that consequently
affects the reproduction performance of the earthworm. Therefore, the outcome
of this study is not only treating sewage sludge into a vermicast that is rich
in nutrients but also production of tiger worm biomass that is of high commercial
Weight of vermicast: The net weight of harvested vermicast was found to be merely equivalent with the sewage sludge fed to the worms. As shown in Table 3, almost 93% sewage sludge has been converted into vermicast during the 21 days of vermicomposting. It seems that each day every tiger worm eats biomass that equal to their mass body weight. That means, for 1000 g earthworms eat almost about 1000 g feeding material to the bin each day. This conversion rate is significant and roughly can be taken as the projection rate of vermicast for bigger scale vermicast production.
Municipal sewage sludge is normally treated in a stabilization pond and will
be dumped in a landfill. Such activities require extensive energy and cost of
treatment and handling. Instead of being conventionally treated and land filled,
this sludge is possible to be converted into vermicompost or biofertilizer which
is found to be rich in nutrients for plantation activity. The present study
inferred that sewage sludge can be reused and retreated as good quality fertilizer
for agricultural purposes. Results of this study indicate vermicomposting is
useful for treating the nutrient rich sewage sludge into a high value commodity
such as biofertilizer besides producing biomass of tiger worm that is of high
commercial value. Vermicomposting has been found capable in enriching the element
content of phosphorus, potassium and nitrogen contents of sewage vermicast.
Subsequently sewage sludge could be utilized as a biofertilizer which could
act as an efficient soil conditioner for sustainable land restoration practices
and fertilizer substance that is biodegradable as opposed to chemical synthesized
that is obviously harmful to the environment.
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