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Risk Analysis and Optimization of Fishing Port Waste Water Treatment Plant Using Fault Tree Analysis Method
Diki I. Perdana* and Nieke Karnaningroem
Department of Environmental Engineering, Faculty of Civil Engineering and Planning, Institut Teknologi Sepuluh Nopember (ITS) Surabaya, 60111, Indonesia
Received: October 23, 2016 Accepted: January 1, 2017
ABSTRACT
This research will analyze the potential risks that will jeopardize the performance of fishing port Waste Water Treatment Plant (WWTP) and propose an optimization strategy. The variables of the analysis are human resource capacity, machinery and tools, and wastewater treatment process. The operations of WWTP will be analyzed using Failure Mode Effect Analysis (FMEA) to discover the factors of potential risks. The risks will then be scrutinized to find out the true causes of the problems using Fault Tree Analysis (FTA) method and be calculated on the value of probability and its consequences to determine into which category in the risk matrix that they will fall. Pursuant to the risk matrix, an optimization will be strategized by mitigating the risks.
Optimization priority will be given to those with the category of Severe and High. The major causes of decremental effluent quality reside on the factor of machinery and tools i.e. defective flow meter and hydroextractor; the factor of wastewater treatment process i.e. the value of BOD loading, recirculation ratio, airflow, and the substandard efficiency of the aeration tank; and the factor of human resource i.e. the inadequate capacity of the technicians due to absence of training on wastewater treatment and WWTP operations.
KEYWORDS: Risk Analysis, Failure Mode Effect Analysis, Fault Tree Analysis, Wastewater Treatment Plant (WWTP), Optimization.
INTRODUCTION
Pelabuhan Perikanan Samudera Nizam Zachman Jakarta is the largest fishing port in Indonesia of which industrial zone is packed with small- to large-scale fish processing business entities. Their wastewater contains high organic matter [1], and the level of pollution very much depends on the type of processing and of the processed raw material [2]. The fishing port Wastewater Treatment Plant (WWTP) applies biological treatment using activated sludge technology, with the maximum treatment capacity of 1.000 m3/day, the wastewater contains maximum BOD 500 mg/l and TSS of 500 mg/l [3]. Data of periodical inspection on the quality of the WWTP effluent from 2013 to 2015 demonstrate that 87% of the effluent do not meet the standard quality. A number of factors have caused the failure and measures have been taken to address the issue, however they have yet to increase the WWTP performance as targeted.
Therefore, methods for risk identification and analysis are needed. Some of the commonly used ones are Failure Mode Effect Analysis (FMEA) and Fault Tree Analysis (FTA). Both can be used as an instrument to develop a process, product, or service [4]. To obtain an optimum condition, the identified risk will be analyzed to determine and measure, as well as assess each of the elements of problem-causing factors [5]. Fault Tree Analysis has ability to analyze system failure and to determine risk-causing factors from the smallest element [5], [6], [7], [8] and [9]. The risk factors will be measured and assessed by considering their probability and consequences. Risk assessment is important in determining risk category based on risk matrix [10].
The objectives of this research are evaluating the WWTP operations and identifying factors that have caused the failure; and analyzing risk category and determining priority for optimization in order to optimize the WWTP treatment and operation performances. If the WWTP operations and treatment performances are optimum, the effluent quality will meet the standard quality and reduce the level of pollution in the receiving waters.
MATERIALS AND METHODS
In this research, the risk analysis and performances optimization are carried out using descriptive quantitative method. Research activities include field observation on the WWTP operations, effluent sample testing, questionnaire and interview, evaluation of the WWTP performances, and data analysis and interpretation. The data collected for risk identification and determination are:
1. WWTP Planning/Design documents.
2. WWTP Standard Operating Procedure or Operation and Maintenance Manual.
3. Sampling and effluent quality testing according to standard quality [11].
4. Daily operation report of the operator and technician (malfunction and troubleshooting).
5. Maintenance, repair, and replacement of WWTP machinery and tools.
6. Personnel Data, Job Description and Personnel Workload Analysis.
7. WWTP operation and maintenance budget.
The risk identification steps using FMEA method are: a. reviewing every unit of process in WWTP, b.composing Fishbone Diagram for the reviewed aspects, c. identifying risk by taking into account affecting factors, and d. validating and determining risk as top event. Next, risk analysis is conducted using Fault Tree Analysis method which comprise of two steps: a. quantitative analysis i.e. composing Fault Tree diagram and b.
quantitative analysis which includes value of Probability, Likelihood and Consequence.
Table 1. Criteria of Probability or Likelihood Value
Category Description Value Range
Rare The performed activities rarely cause risk to the environment <10%
Unlikely The performed activities may cause risk to the environment 11 – 30%
Moderate The performed activities will possibly cause risk to the environment 31 – 60%
Likely The performed activities will probably cause risk to the environment 61 – 80%
Almost Certain The performed activities will cause risk to the environment >81%
Source: [10]
Table 2. Criteria of Consequences Value
Category Description Value Range
Negligible Risk consequences to the environment are insignificant <10%
Low Risk consequences expose minor negative impact to the environment but, in order to reduce possible risk, necessary actions such as on-site troubleshooting are needed
11 – 30%
Medium Risk consequences expose intermediate negative impact to the environment, thus management based on normal procedure is needed
31 – 60%
High Risk consequences expose major negative impact to the environment, thus intensive management measures are needed to tackle the issue
61 – 80%
Extreme Risk consequences are very destructive to the environment >81%
Source: [10]
The obtained risk value will be evaluated based on the category of risk level [9] and cross-checked in the risk map. Risk of highest level will be given priority for optimization.
RESULTS AND DISCUSSION
A. Risk Identification
The purpose of risk identification is to recognize any possible risks so that the system can be optimized by preventing or minimizing the event. Based on data, interview, and observation, it can be identified that risk factors are human resource, machinery and tools, and wastewater treatment process. The benchmark for WWTP performance failure is the decremental effluent quality which goes below the standard quality [11].
In each of the risk factors, there are several risk subfactors that influence the value of risk factor.
Figure 1. Fishbone Diagram of WWTP Decremental Effluent Quality
B. Risk Analysis and Evaluation
Determining Probability and Likelihood
The probability calculation is done by plugging the value of frequency of event and frequency of process that have been determined from each of the components of root events into the following formula:
∑ where:
P : Probability
Fp : Frequency of Process Fk : Frequency of Event
The result of the probability calculation on each factor and subfactor will then be plugged into a mathematical formula which is an expression of quantitative logic of Fault Tree qualitative analysis to have the value of likelihood.
Mathematical formula for factor of human resource (HR) is as follows:
P HR = P quantity + P quality + P job description + P guidance & supervision
= {P operator + P technician + P analyst} + {P education + P expert + P operation} + {P SOP + P unfeasible of SOP + P implementation of SOP} + {P person in charge + P work report + P assestment of performance}
= {P operator + P technician + P analyst} + {P education + P expert + (P training x P literature)}+ {P SOP+ (P tools x P method) + P implementation of SOP} + {P person in charge + P work report + (P evaluation+ P sanction)}
Figure 2. Fault Tree Diagram of Factor of Human Resource
Figure 3. Fault Tree Diagram of Factor of Machinery and Tools
The following is the mathematical formula for the factor of machinery and tools:
P Machinery &Tools = P manhole pump + P flowmeter + P blower + P diffuser + P lift pump + P sludge circulation pump + P hydroextractor
= {P condition/function+ P spare part+ P lifetime + P maintenance} + {P condition/function + P spare part + P repair} + {P condition/function + P capacity + P spare part + P lifetime + P maintenance} +
{P condition/function + P placement + P maintenance} + {P condition/function + P spare part + P lifetime + P maintenance} + {P condition/function + P spare part + P lifetime + P maintenance} + {P condition/function + P spare part + P repair}
= {P condition/function + P spare part + P lifetime + P maintenance} + {(P jammed x P out of order) + P spare part + P repair} + {P condition/function + P capacity + P spare part + P lifetime + P maintenance} + {(P clogged x P out of order) + P placement + P maintenance} + {P condition/function + P spare part + P lifetime
+ P maintenance} + {P condition/function + P spare part + P lifetime + P maintenance} + {(P nonoperational x P out of order) + P spare part + P repair}
Figure 4. Fault Tree Diagram of Factor of Treatment Process Mathematical formula for the factor of treatment process is as shown below:
P process = P buffer tank + P aeration tank + P sedimentation tank
= {P td} + {P BOD loading + P air required + P aeration time + P RAS + P efficiency} + {P td + P efficiency}
= {P Q x P volume} + {P BOD loading + P air required + P aeration time + P RAS+ P efficiency} + {P td + P efficiency}
Determination of Consequence
Consequence is an effect/impact of an event that is usually expressed as a loss caused by that event.
The value of Consequence is obtained from the calculation of each of the factors in the Fault Tree Diagram.
The result will then be categorized according to the range of value attained from the value of Consequence/the largest impact with the category of Extreme observed in the factor of Machinery and Tools (Flowmeter and Hydroextractor components) and factor of Treatment Process (Aeration Tank components).
Risk Mapping
The results of the calculation of Likelihood and Consequence are plotted into a matrix of risk level category with Consequence on the X-axis and Likelihood on the Y-axis. The plotting will then become the risk map which will serve as the basis for designing strategy for optimization action.
Table 3. Recapitulation of Risks Assessment
Risk Factor Subfactor Level 1
Subfactor Level 2
Subfactor Level 3
Category of Probability
Category of Consequence
Category of Risk
Human Resource
Quantity
WWTP Operator Likely Medium Major
Mechanic and Electrician
Likely Medium Major
Laboratory Analyst
Almost Certain Medium High
Quality
Education Level Likely High High
Expert Moderate High Major
Comprehension on WWTP Operations
Training Almost Certain High Severe
Reference/
Literature
Likely High High
Job Description
Set of SOP Likely Medium Major
Unfeasible SOP Tools Almost Certain Medium High
Methods Likely Medium Major
Implementation of SOP
Almost Certain Medium High
Guidance &
Supervision
Person in Charge Likely Medium Major
Work Report Likely Medium Major
Assessment of Performance
Evaluation Likely Medium Major
Sanction Almost Certain Medium High
Machinery and Tools
Inlet Pump (Manhole Pump)
Condition/
Function
Likely Low Significant
Spare Parts Likely Low Significant
Pump Lifetime Moderate Low Moderate
Maintenance Likely Low Significant
Flowmeter
Condition/
Function
Jammed Unlikely Extreme Major
Out of Order Almost Certain Extreme Severe
Spare Parts Almost Certain Extreme Severe
Repair Almost Certain Extreme Severe
Blower
Condition/
Function
Likely Low Significant
Capacity Likely Low Significant
Spare Parts Likely Low Significant
Blower Lifetime Moderate Low Significant
Maintenance Likely Low Significant
Diffuser
Condition/
Function
Clogged Likely Low Significant
Out of Order Moderate Low Moderate
Placement Moderate Low Moderate
Maintenance Moderate Low Moderate
Lift Pump
Condition/
Function
Likely Low Significant
Spare Parts Likely Low Significant
Pump Lifetime Moderate Low Moderate
Maintenance Likely Low Significant
Sludge Recirculation
Pump
Condition/
Function
Moderate Low Moderate
Spare Parts Moderate Low Moderate
Pump Lifetime Moderate Low Moderate
Maintenance Moderate Low Moderate
Hydroextractor
Condition/
Function
Non Operational Almost Certain Extreme Severe
Out of Order Unlikely Extreme Major
Spare Parts Almost Certain Extreme Severe
Repair Almost Certain Extreme Severe
Process
Buffer Tank Detention Time
Influent Discharge
Moderate Negligible Trivial
Tank Volume Unlikely Negligible Trivial
Aeration Tank
BOD Loading Almost Certain Extreme Severe
Air Intake Likely Extreme Severe
Aeration Time Moderate Extreme High
Circulation Ratio Almost Certain Extreme Severe
Efficiency Likely Extreme Severe
Sedimentation Tank (Clarifier)
Detention Time Almost Certain Negligible Trivial
Efficiency Likely Negligible Trivial
Table 4. Map of Risk Category
Human Resource
Consequence
Extreme High Medium Low Negligible
Likelihood
Almost Certain
Severe Severe High Major Trivial
Out of Order, Spare Parts & Repair
(Flowmeter) Non Operational
(Hydroextractor) BOD Loading Sludge Circulation Ratio
Training Laboratory Analyst Tools Implementation of SOP Sanction
Likely
Severe High Major Significant Trivial
Air Required Efficiency (Aeration Tank)
Education Level Reference/
Literature
STP Operator Mechanic &
Electrician Set of SOP Method Person in Charge Work Report Evaluation
Condition/Function, Spare Parts &
Maintenance (Inlet Pump)
Condition/Function, Spare Parts &
Maintenance (Blower) Clogged (Diffuser) Condition/Function, Spare Parts &
Maintenance (Lift Pump)
Efficiency (Clarifier)
Moderate
High Major Significant Moderate Trivial
Aeration Time Expert
Lifetime (Inlet Pump) Lifetime (Blower) Out of Order, Placement
& Maintenance
(Diffuser) Lifetime (Lift Pump) Condition/Function, Spare Parts, Lifetime &
Maintenance (Sludge Circulation Pump)
Effluent Discharge
Unlike
Major Significant Moderate Low Trivial
Jammed (Flowmeter) Out of Order
(Hydroextractor)
Tank Volume (Buffer Tank)
Rare Significant Moderate Low Trivial Trivial
C. Optimization Action
The method that will be used for optimization is risk mitigation. Risk mitigation is risk management with the strategy to reduce the frequency of risk events and prevent the emergence of other risks. The optimization is focused more on the last level of subfactor (minimal cut set), or on the problem-causing root as identified with FTA method.
Mitigation strategy is carried out by taking into account the scale of priority. The recommendations are actualized starting from the highest risk criterion (Severe) which imposes the largest potential in decrementing the WWTP performances. Next, the optimization is performed gradually for risks with the category of High and Major by of course considering availability of budget.
Table 5. Recommendation and Estimation of Optimization Cost (Risk Category of Severe and High)
Risk
Category Recommended Mitigation Plan Requisite/Investment Cost (IDR) Outcome
Severe
Routinely sending relevant personnel to technical training of WWTP operations
- Training of Wastewater Treatment and WWTP Operations (6 personnel @ once/year)
30,000,000
Increased proficiency and skill of the personnel which will result in better performance - Courses for Mechanic and
Electrician (6 personnel @ once/year)
15,000,000 Replacing Flowmeter with the
one needed and specifically designed to endure the WWTP environment
- Sewage Hi-Flowmeters (1 unit for reserve)
30,000,000
Known effluent intake so that WWTP treatment load is assessable Supplying fast-moving spare
parts of the Flowmeter
- Flowmeter maintenance (quarterly)
600,000 Conducting periodical
maintenance and repair of Flowmeter every month
Proposing the reactivation of hydroextractor operation
- Filter Press machine repair 250,000,000
Hydroextractor being able to treat sludge, by-product of biological process, which is usually dumped and pollutes the waters Supplying fast-moving spare
parts
- Spare Parts of machinery and electrical tools
30,000,000 Conducting periodical
maintenance every month
- Machinery and tools maintenance (12 months, @ IDR 5.000.000,-)
60,000,000 Routinely monitoring and
assessing BOD load intake and soliciting industry to pretreat their effluent
- Portable COD meter
8,500,000
Known intake load to WWTP to prevent shock loading of the process
Replacing DO meter monitoring device for out-of-order DO meter, ORP & pH meter and monitoring the performance of the blower & hyper rater
- Tools/sensor of DO meter, ORP and pH meter including monitor
25,000,000
Managed work of the blower to keep oxygen transfer at desirable rate Controlling, monitoring and
daily registering the process of active sludge recirculation (20- 40%)
- Automatic sensor and timer of sludge circulation pump
500,000
Maintained number of microorganisms in aeration, extended sludge lifetime, and better process efficiency Monitoring and maintaining
processes criteria at designed criteria by conducting periodical assessment/calibration and registration
WWTP treatment
performance in desired target and consistently maintained effluent quality
High
Employing a Laboratorium Analyst
- Recruiting personnel (1 person, 13 months of salary)
43,550,000
More frequent and routine analysis of effluent quality Replacing and/or hiring more
operators based on evaluation of performance & competence
- Hired personnel
having the needed competence and skills Enriching references/literature
relevant to WWTP processes and operations
Increased knowledge
and understanding of the operators and technicians Procuring necessary tools as
mentioned in the SOP
- Mechanical and electrical working tools
30,000,000
Better performances of the operators and technicians that will increase their productivity Conducting regular monitoring
and supervision to WWTP operators
- Monthly Meeting of Coordination and Evaluation (meeting consumption for 15 people x IDR 50.000,-)
9,000,000
Evaluated performance, discussion and problem solving, and maintained communications and relations among personnel Imposing sanction based on
applicable personnel regulations
Increased work
discipline and compliance of the operators Monitoring and assuring that
effluent intake does not exceed the WWTP capacity (1000 m3/day) and filling out logbook on daily basis
Available data of
daily effluent discharge and status of WWTP treatment capacity
Total Cost 532,150,000
CONCLUSION
Risk factors which influence the operations of WWTP are human resource, machinery and tools, and treatment process. Risk with the category of Severe can be observed in the following subfactors: absence of training for personnel, damaged Flowmeter without further repair and availability of spare parts, nonoperational and unmaintained hydroextractor, BOD loading exceeding WWTP capacity, unqualified air required and sludge circulation ratio, and low processing efficiency of aeration tank. Optimization action is prioritized for risk with the category of Severe and High with estimate cost of IDR 532.150.000,-.
ACKNOWLEDGMENTS
The authors would like to express their gratitude to the Ministry of Marine and Fisheries of the Republic of Indonesia, for granting the scholarship and fund for this research.
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