For the Batu Maung pig estate, we suggest four solutions for the waste-water management:
| Solution 1 | - | Based on present situation of development, using the existing terrain. |
| Solution 2 | - | Using part of the reclaimable mangrove swamps. |
| Solution 3 | - | Using also reclaimable mangrove swamps but a larger area. |
| Solution 4 | - | Based on the proposed development plan for Bayan Lepas with an initial phase using the present situation (this first phase is similar to Solution 1) and a second phase with full operational capacity. |
There is one common prerequisite to all solutions: As the conveying of the total pig waste material would be too costly and as the management of this would be too difficult in Batu Maung, first of all, well designed sedimentation tanks must be constructed. These sedimentation tanks should be constructed near the road, facilitating the transport from these tanks for manuring purposes in the field, or the transport of the digested sludge from the biogas plants, having a capacity for digestion of waste of 5 000 pigs each.
The volume of the sedimentation tanks should be planned according to the pig population calculating about 20 liters per pig and for solids 5–10 liters per pig. That means 125–150 m3 settling tank would be enough for 5 000 pigs. If it is combined with biogas production, the settling tank could be about half this size. The bottom of the setting tank should have a steep slope. toward one corner from where the solids can be removed with a suitable sludge pump. Some basic construction data for construction cost estimation are given in ANNEX C.
With the construction of a sedimentation tank of adequate size and design, 95 percent sedimentation of the solids will be achieved. For the construction data, a monthly sludge removal is assumed, which might be less or more frequent, depending on the cleaning practices.
Fishponds can be constructed according to our first alternative in the bed of the existing canal (Fig. 9.3). As the canal system is presently filled with settled solids of the pig wastes, it has to be removed using either suitable pumps or dozers. For a rough cost estimation, see ANNEX D. The bed of the canal system has to be excavated further so that about 1.5 m deep water can be kept in the ponds to be constructed.
The excavated soil can be used to strengthen the existing dam on the mangrove side of the canal or for the construction of a 1 m high dam along the other side of the canal (Fig. 9.3), and the cross dams if the site is found suitable.
For the construction of the dividing dams, pre-fabricated concrete slabs are recommended. A rough estimation of the dredging and construction costs are given in ANNEX D.
To avoid inundation of the housing and pig estate area, a run-off drain has to be constructed along the planned longitudinal dam (Fig. 9.3). The pig estate and housing area covers about 38 hectares. Calculating 100 mm precipitation from a heavy rain in one day, the drain has to transport a maximum of 38 000 m3 water. Exact calculation for the drain measurements has to be based on meteorological data for this area and be made by a competent engineer.
If the ponds can be excavated to a sufficient depth, so that the 1 m high drain is not needed, the whole pond system can be used as drainage canal. In this case, ca. 0.5 m deep and 1 to 1.5 m wide spill gates will be left in the dividing dams, applicated with an iron rod screen to avoid the escape of fish. The two reservoirs (Fig. 9.4) will initially collect the waste water coming from the sedimentation tanks during the whole day, but mainly during cleaning process in pig sties. From these reservoirs, the waste liquid will regularly be applied to the fishponds (See Item 5.4). Electric pumps will be installed in a pump stand in the reservoirs. For the capacity of the pumps, it should be taken into consideration that the drainage system, i.e. the reservoirs, collect household sewage as well. This is an unknown factor. The average sewage volume for a bathroom equipped household is ca. 200 1/day/person in Europe. The normal quantity of waste water of 20 liters per pig might be exceeded in the case of Batu Maung because the farmers seem to use more water for housing the sties. To secure the distribution of the wastewater within a short time (see Item 5.4) from the reservoir into the ponds, two electric pressure pumps are needed of 30–40 (or even more) 1/sec capacity. Each pump will be placed over a concrete shaft. For the distribution of the wastewater, an irrigation pipeline of 6 inch diameter would best be used, along the longitudinal dams, branching off with 2.5 inch diameter pipes towards the 8 overhead sprinklers distributed along the ponds. Cost estimates are given in ANNEX E. The conversion of the canal system will result in ca. 3.8 hectares fish production pond plus ca. 0.7 hectares reservoir pond. This, however, would only be enough to process - at maximum - about one-third of the liquid waste of the present pig population at Batu Maung.
The advised sequence of the construction should be as follows:
Construction of the sedimentation tanks, possibly also biogas plants.
After completion of (a), dredging the draining canals with suitable sludge pump or dozer.
Excavation of pond bottoms to suitable depths and construction of second longitudinal dam. Simultaneously, construction of cross dams with 80 cm wide sluice gate (which can be closed with two rows of planks). If longitudinal dam not necessary, cross dams have to be constructed with spill gates (1.5 m wide and 0.5 m deep).
Parallel with that, simultaneous the pump stands, shafts can be constructed.
Sequential filling of ponds (1–6 and 6–8) by closing the sluice gates with two rows of planks and the sprinkling of the waste-water can be made.
Stocking of ponds with suitable polyculture fish population (see Item 5.5).
As second alternative, the whole row of ponds could be constructed in the present mangrove growth which will have to be reclaimed in 100 m width and in 1 200 to 1 300 m length. A second longitudinal dam parallel to the present one will then be the seaward dam (Figs. 9.3 and 9.5).
Dredging of the clogged drainage canal will also become necessary, the pond and reservoir construction, apart from the falling of the mangroves, can be calculated with the same cost per unit dam or moving of soil as it was given for Solution 1. The cost estimation is given in ANNEX F. This alternative would result in a pond area of ca. 12 hectares, which is sufficient for the treatment of the liquid of pre-treated wastes of 11 000 to 12 000 pigs.
As third alternative, the ponds can also be widened shifting the already existing longitudinal dam along the mangrove fringe 20 m landwards and reclaiming only 80 m from the mangrove swamps (Figs. 9.3 and 9.6). This solution would leave a narrow but protecting mangrove belt for the seaward dam as long as a strong permanent dam is not completed. As in Alternative 2, the existing canal system along the inner dam, namely the draining trench, can also be maintained. Also here, pond and reservoir construction will be based. on the same costs per unit (See ANNEX G). There will be less mangrove area to be reclaimed, but the inner dam has to be shifted. The resulting pond area is the same as in the second alternative and the same amount of liquid waste can be treated in the ponds.
In this case, fish production ponds will be constructed along the airport. This area which is presently also mangrove swamp, is already identified in the proposed development plan as reclamation area. This alternative suggests a stepwise solution of the waste problem with two phases. During the first phase, the cleaning and utilization of part of the wastewater could be made and plenty of useful experience can be collected.
(i) First phase - the first phase would be very similar to the first solution described above. All construction elements will be the same. After completion of the pond in the reclaimed area, the ponds of this first phase can then be used as freshwater reservoirs for the second phase (or even as additional fishponds). The only difference to the first solution is the lower number of dividing dams resulting in fewer fishponds but larger reservoir area (Fig. 9.7). Reservoir 1 is ca. 10 000 m2 large, Reservoir 2 is ca. 4 000 m2 and the pond will cover ca. 2.9 hectares (Pond 1 ca. 13 400 m2, Ponds 2 and 3 ca. 7 600 m2 each). Pond 1 could also be divided into two, if found necessary, for better management.
(ii) Second phase - After the reclamation of the mangrove swamp in the elongated area along the airport, the ground has to be freed from mangrove roots and levelled. For reason of easier management, it is advisable to construct not more than six ponds in this area. Again, the pond construction follows the already described methods.
The following dam constructions will be necessary: one longitudinal dam of 1 300 m length, as second landward dam the presently existing dam can be used. The dividing dams will be supplied with sluice gates of 0.8 m width. Other construction details and cost estimations are given in ANNEX H. The filling of the ponds is most practically done from a 40–50 cm wide open canal to be constructed on the crown of one of the longitudinal dams through simple pipe inlets.
The reclaimed area will be about 12–13 hectares. On this area, about 9–10 hectare ponds can be constructed: Pond No. 1 = 2.8 ha; Pond No. 2 = 1.6 ha; Pond No. 3 = 1.6 ha; Pond No. 4 = 1.6 ha; Pond No. 5 = 1.6 ha; and Pond No. 6 = 1.6 ha (Fig. 9.8).
It is not known whether a separate pond draining system is necessary. This will depend on the pond draining practice, planned. If the ponds are drained sequentially, and with portable pumps, the drainage construction can be spared. In case, this system is thought necessary, each pond needs a draining gate (monk) preferably in the seaward dam, emptying either directly into the sea or into an open canal connecting all monks.
The transportation of the liquid waste will again be achieved, through an irrigation pipeline, 6 inch in diameter and 12 sprinkler, will distribute each ca. 200 liters of wastewater per minute.
Two modes of sprinkling the wastewater are possible:
Round sprinklers, placed in the ponds on strong support about 0.5–0.75 m above the pond level.
Sector sprinklers, placed on the dividing dams. This ensures an easier access for maintenance.
As described under Item 2.1.1, the geographical situation does allow the construction of fishponds of sufficient sizes. The pollution problem in the bay can be solved through the following ways:
Separation of solid and liquid phases of the waste in settling tanks;
Treating the sludge in biogas units; and
Piping the liquid phase from settling biogas units into the sea or transport by tank trucks to other treatment places.
Two biogas plants should be constructed, one near to the Gertak Sanggul river side and the other near the concrete draining canal. The capacity of the biogas plants would be planned and constructed according to the quantity of wastes conveyed to the corresponding side.
It would be advisable not to allow an increase in the capacity of the piggeries in this area. The liquid wastes discharged from the sedimentation tanks (biogas plants) should be joined and be piped into the sea at least several 100 m from the shore. The length of such a pipeline into the deeper part of the bay will depend on the hydrographical situation in the bay, which is presently not known. The fact that the bay has already become septic indicates that the water exchange is very poor. The bay is indeed very shallow. The 5 m line forms a wide crescent from the Gertak Sanggul cape to the other side at Batu Maung (Fig. 9.1). The tidal currents do not influence enough the shallow part of the bay. Before a decision on the length of a wastewater pipeline are made, the main current characteristics must be measured. This can easily be done with simple drifters followed from a ship, observed from the air or by radar. This should be done over several tidal cycles and in different seasons. The pipe should reach deeper water to secure sufficient dispersion and mixing. However, the distance to the tip of the cape where the 2 m and 5 m lines come close to the shore is approximately 3 km.
If the riverbed is dredged, it might be sufficient to pipe the liquid phase into the stream outlet which will help the wastewater to mix with the bay water. It seems, however, that this is only feasible during the rainy season with enough water flow in the river. With lack of dispersion, the natural biological cleaning capacity will again be impeded and the depletion of oxygen and production of hydrogen sulfide will also occur in the river estuary
Another possibility is the transport of the liquid phase from the biogas plants to other places where fishponds can be constructed or are existing in connection with other pig waste treatment schemes. The establishment of an aeration plant for treatment of the liquid waste is hardly feasible because: (i) the greater space demand of such a plant; (ii) the odour which affects the neighbourhood; (iii) also the half-cleaned wastewater unless piped farther from the seashore will further pollute the shallow parts of the bay; and (iv) it is too costly in regard to a half or unsatisfactory solution.
The exact location for the biogas plants, the layout of the pipes and further the construction of the pipeline into the sea has to be planned and supervised by competent engineers experienced in these fields.
For the necessary hydrological investigation in the southern waters of Penang, especially in the Gertak Sanggul Bay, the assistance of the University Sains Malaysia and the Fisheries Research Institute could be requested.
It is recommended to construct for each bigger piggery its own sedimentation tank of adequate size and design which could withhold most of the solids and supernatant (foamy) parts of the sludge. From each sedimentation tank, the outflowing liquid phase should be conveyed into a recipient pond through a close pipeline system. The collected liquids can then be treated in fishponds or used as fertilizers on nearby land. The terrain seems to have enough slope to convey the wastewater to the recipient ponds by gravity.
It is highly recommended to connect this sedimentation treatment with biogas production which would be at the same time also secure the suitable handling of the sedimentation tank and utilization of the solid parts. In this connection, it is recommended to explain to the farmers the handling and advantages of such a combined treatment.
As mentioned under Item 2.2.2, the freshwater supply is limited by the present capacity of the pipeline. Possibly, surface water during heavy rains can be collected for filling the ponds. Therefore, it seems more reasonable to establish here brackishwater fishponds, which does not pose a space problem. Even with the extension of the pig farming activity, there is still enough space for treatment with fishponds. The problems that arise here are: (i) the established farms are scattered in larger areas. A joint treatment of the wastes will be costly and difficult; (ii) the area is far off from the other habitations, only fishermen village is nearby. The accessibility of the place is time-consuming.
Considering these factors, it is not advisable to start a pilot project in this vicinity.
