Design of Sub-surface Constructed Wetland for Greywater Treatment Using Canna Indica (Case Study: Kelurahan

Untreated greywater is one of sanitation issues that occured in Keputih, Surabaya. In order to manage this sanitation issues, constructed wetland is capable of treating domestic wastewater especially greywater, therefore this method is chosen. Design of constructed wetland is projected for 2019 until 2028 usage. Characteristics of greywater influent is typically: BOD 190,43 mg/l; COD 289,17 mg/l; TSS 206,67 mg/l. Canna indica is selected for this treatment due to maintenance value. Apart from constructed wetland design, standard operating procedure and bill of quantity is also made. From this design, the grewater effluent quality is estimated: BOD 30 mg/l; COD 46,28 mg/l; TSS 26,67 mg/l thus meet the Domestic Wastewater Quality Standard from East Java Governor Regulation No. 7 2013. The cost required to build CW in Kelurahan Keputih Surabaya is Rp 9.156.412.000.


Introduction
In 2012, there are 3.040 and 1531 people suffered from skin disease and diarrhea due to bad sanitation in Keputih, Surabaya respectively.This happened because untreated domestic wastewater is polluting the river [1], therefore wastewater treatment that suitable with the region is needed.Keputih has ex-landfill area of 40,5 Ha which has been closed in 2001, and allocated as green area in city development plan [2], thus ex-landfill area in Keputih is selected.
Method of treatment in this design is constructed wetland using Canna indica as its main vegetation.Constructed Wetland is controlled treatment system design and built around natural process (vegetation).This vegetation includes sandy soils and microorganism for wastewater treatment.Constructed wetland cost less than conventional wastewater treatment in term of both investation and maintenance cost [3].Constructed wetland also has 97% removal of TSS [4], odorless [5] and has high value of aesthetics [6].There are two types of Constructed Wetland, surface flow and sub-surface flow.Surface flow Constructed Wetland could increase mosquito population around constructed Wetland area, thus makes sub-surface constructed wetland is more suitable in Indonesia [7].Sub-surface Constructed Wetland utilize natural symbiosis between vegetation and microorganism in the area [8].

Design Methods
Methods used in this design is unit dimensions calculation, BoQ calculation, and standard operating procedure of treatment unit.Unit dimensions calculation is based on greywater quality and quantity in Keputih.Greywater quantity (flow) calculation depends on clean water usage per person while greywater quality is based on laboratory analysis.Methods of analysis to determine greywater quality [11] is shown in Table 1.

Keputih Population Projection
Design periods of this Constructed Wetland is 2019-2028, while 2016-2018 is the initial years of this Constructed Wetland.There are 3 methods to calculate population projection, arithmetic, geometric, and least square.The selected method is one with correlation factor closest to 1 and lowest standard deviation value [12].Data used for population projection is population data from 2011-2015.Based on the calculation, population of Keputih in 2028 is projected about 26.982 people.

Greywater Quality and Quantity Determination
Greywater quantity is determined from Keputih citizens water bill (per house) about 164,5 L/person.daywhile 75% of those fresh water turned out to be greywater [13].Calculation of greywater quantity is as follows: Qave fresh water = fresh water usage/person.day× population (1) Qave greywater = 75% × Qave fresh water Based on ( 1) and ( 2) equations, greywater quantity in Keputih year 2028 is 3.329,29 m 3 /day.Greywater quality obtained from laboratory analysis is shown in Table 2.

Unit Dimensions Calculation
Constructed Wetland in this design is also equipped with 1 unit of collecting basin and 3 units of indicator basin.Collecting basin function is to collect greywater before entering Constructed Wetland while indicator basin serves to test greywater effluent with biological indicator (fish) before entering river.Collecting basin dimension is designed 4 x 4x 3,3 m (length x width x height) while indicator basin dimensions is designed 12 x 6 x 2,3 m (length x width x height).Design criteria for Constructed Wetland is as follows:  TSS Removal: 60 -75% [5]  BOD Removal (by media) : 75% -98% [14]  BOD Removal (by vegetation): 4,4% [15]  HLR: 0,2 -1 m 3 /m 2 .day[16]  Length : width ratio: 4:1 -10:1 [13] The equation used for this design is as follows [17]: There are 6 constructed wetland designed with 0,6 media depth m and 0,01 slope.Media depth is adjusted according to Canna indica root that can grow up to 0,6 m.Media used in this constructed wetland is medium gravel whose Ks value is 5000 m 3 /m 2 .day,alpha = 0,4 and k20 = 1,104 [5].Effluent must comply with regulation, BOD < 30 mg/l, COD < 50 mg/l, TSS < 50 mg/l and pH 6-9.Degradation process in Constructed Wetland not only occurs in media, but also in vegetation and rhizobacteria.Rhizobacteria lives in collony and together with rhizome.It uses greywater as food source.Constructed wetland with vegetation (planted) has higher value of BOD removal (higher 4,4%) than the unplanted one [15].The function of plant in Constructed Wetland provides hydraulic line in media and to keep greywater conductivity stable [18].

BoQ (Bill of Result Calculation
Along with 6 constructed wetlands, 1 unit of collecting basin and 3 units of indicator basin is also designed.Total expenses for all of treatment units is 9.156.412.000rupiah.

Table 1 .
Methods used for Greywater Quality Analysis Effluent standard used in this design is the Domestic Wastewater Quality Standard from East Java Governor Regulation No. 7 year 2013.BOQ calculation is based on Harga Satuan Pokok Pekerja (HSPK) Surabaya City 2015.