Analysis of the distribution of domestic wastewater in the Brantas river area of Malang city

The degradation of water quality has become a major problem today. In Indonesia, the decline in water quality is caused by domestic wastewater which is a non-point source. In an effort to reduce the occurrence of environmental degradation due to domestic wastewater, it is necessary to give an idea and convince the public and the relevant parties of the importance of domestic wastewater management. Efforts are made by informing the pattern of distribution of domestic wastewater in a region and the impact of its distribution for its control and management. The research method uses a momentary sampling technique in accordance with SNI 6989.59:2008. The location of the water sampling is determined purposively. Sampling was conducted in two periods; the dry season in September and the rainy season in January. The observed parameters included BOD5 and E.coli. Determination of the distribution of domestic wastewater uses GIS. The distribution of domestic wastewater is determined based on pollution levels expressed as IP. The results show that pollution levels in Sawojajar and Sumbersari were lightly polluted with average IPs of 4.09 and 4.02 (dry season). While Kedungkandang is in the good category, IP = 0.32 (dry season).


Introduction
Degradation of water quality becomes a big problem in the world because water is the core of life that cannot be replaced [4].As a result, there are a series of environmental problems, such as water shortages and water damage in ecological systems.One of the causes of declining water quality in Indonesia is the influx of waste discharges of both liquid and solid waste coming from households, hotels, restaurants and so on, commonly called domestic waste into the environment.Domestic wastewater has dispersed properties and is not easily identified and characterized so that mapping and analysis of pollutant sources, load calculations to reveal the impact of human activities on pollution caused.Its spreading nature makes it difficult to observe directly.However, as an effort to reduce the occurrence of environmental degradation due to domestic wastewater, we need a way to provide an image and convince the community and stakeholders about the importance of domestic wastewater management.Therefore, one of the efforts that can be done is to provide an understanding of the pattern of distribution of domestic wastewater in a region.With the knowledge of the distribution of domestic wastewater and the impact of its dissemination, it is very useful in the control and management of domestic wastewater.

Methodology
The research method used the technique of instantaneous example (grab sample).The sampling method is conducted in accordance with SNI 6989.59:2008 [2].The location of the water sampling is determined purposively taken in the districts of Sawojajar, Sumbersari and Kedungkandang.The water sampling points in the drainage channel are determined with the consideration that the location of the water sampling is the flow of liquid waste from various activities of the population's activities that flow into the drainage channel.Sampling was conducted in two periods: dry season in September 2017 and rainy season in January 2018.Parameters observed included pH, BOD5 and E.coli.Determination of the distribution of domestic wastewater used GIS [3].

Determination of quality status water quality
The method used to determine the quality of domestic wastewater in the research location is to compare the water quality of the laboratory test results with the established quality standard that is in accordance with the East Java Governor Regulation No. 72 of 2013 on the Quality Standards of Domestic Waste Water (Real Estate), Restaurants (Restaurant), Offices, Commerce, Apartments, Hospitality and Dormitory [1].The status of water quality is determined using the Pollution Index Method, with the Sumitomo and Nemerow formulas [7].
(1) 2 where: IPj = pollution index for designationj, Ci = concentration of water quality parameteri, Lij = concentration of water quality parameter i listed in raw designation of water j, M = maximum, R = average From the results of IP calculations, the category of Pollution Index is determined based on the calculation results with the following criteria: a. 0 ≤ IP ≤ 1,0 = good b.1,0 < IP ≤ 5,0 = slightly polluted c. 5,0 < IP ≤ 10 = fairly polluted, d.IP > 10,0 = heavily polluted.

Mapping
The mapping of quality of domestic wastewater of Malang City is done by entering the parameter data collected through field observation / measurement and the laboratory analysis result into the distribution map of domestic waste water pollution.The data input method is supported by land system maps.Color coding is then performed to determine the status of the quality of domestic wastewater.Color codification on the map is used to determine the status of the quality of the domestic wastewater of the observation area.Four color codes used in the mapping, can be seen in Table 1.

Results and discussion
Domestic wastewater distribution research is conducted by identifying the source of domestic liquid waste coming from people's houses through field observation and quality tests of domestic wastewater.Based on field observations, the domestic liquid waste management system in Malang has not been well coordinated.Domestic wastewater dumps are mixed together with drainage channels.The existing drainage system boils down to not being absorbed into the river.In Indonesia the network system usually follows the road network system.So, the network picture of the drainage system in the research area follows the road network system.The drainage system observed is a drainage system located on the main road (primary drainage).
Basically, drainage systems in all three research sites show the same physical characteristics.In the form of open drainage, made of trapezium-shaped brick pairs or rectangles, where the bottom is a layer of soil that is expected to drain water into the soil.Field observations show that not all drainage channels are functioning properly.Some locations, especially in Sawojajar Urban Village, drainage water flow tends to not flow or is blocked due to the amount of garbage or other dirt that was brought by the water.Even at some point, water does not flow and just clumps, resulting in a smell and the color of the water turning solid black.In the dry season, at some locations the direction of flow cannot be observed because the channel is dry.The same thing can be found in the rainy season because the water flowed quite swiftly, but after the rain stopped, the sewer dries up again.
To determine the distribution of domestic wastewater, the distribution of blocks was based on the drainage network and flow direction.This is done to get such that the quality of the test results of liquid waste actually originated and represents the research area.The block division map is shown in Figure 1.

Determination of the quality of domestic liquid waste and the status of water quality.
The quality of domestic wastewater is taken from each sampling point and tested in a water quality laboratory to determine the content of BOD and the pH.From the test results, calculations were made to determine the status of water quality in each study area.The status of water quality is determined using the Pollution Index Method [7], with the Sumitomo and Nemerow formulas.Water quality test results and calculation of water quality status can be seen in table 2. The value pollution index (IP) is used to predict the distribution of domestic wastewater of the research area described in the form of a wastewater dispersion map.An image of domestic wastewater dissemination is shown in Figures 2 through 4.
The result of the observation shows that the pH parameters in both dry and rainy season in the three study areas still meet the standard of quality.For the BOD parameter, the district of Kedungkandang is not yet included in the polluted category, both in the dry season and rainy season.During the dry season, in the district of Sawojajar, the pollution level was found to be in the fairly polluted category in three locations, namely block 2, 3, 11 and 1 i.e. block 11 in the rainy season.While the other blocks show the level of slightly polluted.Although included in the category of slightly polluted, one needs to be wary because the average value of IP in the district of Sawojajar is relatively high at 4.09 from the limit specified to be below 5. Pollution in district of Sawojajar, possibly caused by the discharge of domestic wastewater directly to the drainage without any processing or by wastewater that went through processing that has not met the standards.This condition is supported by the high content of E.coli in water samples tested together with BOD parameters.The findings in blocks 2 and 3 were 85 and 143.50 MPN / 100 ml (dry season) and block 11 it was 295.30MPN / 100 ml (dry season) and 30 MPN / 100 ml (rainy season).A striking difference is seen in the taking with different time periods.Which that the dry season is greater than the rainy season, indicating that the amount of rainwater that goes into the drainage channel affects the water quality in the drainage channel.This condition is seen in blocks 2 and 3 that changes from contaminated moderate in the dry season to be mild in the rainy season.From observations in the district of Sumbersari, it was found that block 1 has the level of fairly polluted in both dry and rainy season.Suspects for other blocks fall into the category of slightly polluted.However, one should be more vigilant because the average IP approaches the safe threshold of 4.02 in the dry season.The results of observation on the content of E. coli bacteria in water samples in block 1 showed 100 MPN / 100 ml, the highest among other blocks.This reinforces the suspicion of domestic wastewater disposal, especially from septic tanks discharged directly into drainage channels or have not met the standards in their management.The district of Kedungkandang is the third research area where observation of the distribution of domestic wastewater was conducted.From the parameters of pH and BOD observed, the district of Kedungkandang belongs to the category of fulfilling the quality standard (blue), averages are IP = 0.32 (dry) and 0.28 (rainy).However, block 4, at the sampling point found E.coli of 33 MPN / 100 ml (dry) and 54 MPN / 100 ml (rainy).Block 4 is the estuary of the previous sampling points.This indicates that the more the estuary is (downstream) the greater the occurrence of pollution.This shows that the accumulation is in the upstream region.If this condition is allowed, then the pollution will increase and the greatest impact will be felt for the community in the upstream area (estuary).

Table 1 .
Color code mapping of pollution level of domestic liquid waste river of Brantas River Malang City.