Investigation of municipal wastewater treatment by agricultural waste materials in locally designed trickling ﬁ lter for peri-urban agriculture

A pilot scale trickling ﬁ lter system was designed, developed, and operated using a constant recirculation method for treatment of municipal wastewater. The maize cob (TF1) and date palm ﬁ bre (TF2) were used as bio ﬁ lm support media in a trickling ﬁ lter system. Both the TF1 and TF2 were compared based on the removal ef ﬁ ciency of pollution indicators such as biological oxygen demand (BOD), chemical oxygen demand (COD), total dissolved solids (TDS), total suspended solids (TSS), electrical conductivity (EC), total nitrogen (TN), total phosphorus (TP) and sulphates. The hydraulic ﬂ ow rate and loading were set as 0.432 m 3 /h and 0.0064 m 3 /m 2 .minute, respectively at temperature range of 15 – 42 (cid:1) C for 15 operational weeks. Both the TF1 and TF2 showed acceptable removal ef ﬁ ciency (61% to 76.3%) for pathogen indicators such as total count, fecal coliform and E-Coli. However, 8 – 15% higher removal ef ﬁ ciency was observed for TF1 for all the pollution indicators as compared to TF2. The results suggest that both the bio ﬁ lm support media in trickling ﬁ lter have potential to treat municipal wastewater in peri-urban small communities to produce environmentally friendly ef ﬂ uent.


INTRODUCTION
Rapid urbanization, industrialization and extensive agricultural activities are exerting colossal pressure on water quality status of Pakistan due to increased wastewater disposal and reuse (Noreen et al. ; Wu et al. ). The existence of combined sewers for domestic and industrial effluents is also increasing the water pollution multifarious.
It is estimated that 7.5708 × 10 6 m 3 of wastewater is being disposed to receiving water bodies for every day in Pakistan (Ali et al. ; Khan et al. ). This increased the pollution in water environment and impacted ecological health including humans, aquatic biota, animals, and agriculture.
So, it becomes essential for planers to treat wastewater before disposal or reuse. Wastewater treatment (WWT) refers to removal of contaminants from the wastewater for production of environmentally friendly effluent for safe disposal and agricultural reuse (Licciardello et al.; ). It is estimated that about 10-20% of all the wastewater generated in developing world receives treatment and the rest being discharged to receiving water environment without treatment (Rasool et al. 2017). Similarly, in Pakistan, the status of WWT (6-8%) is poor assuming all existing treatment systems operation at their full designed capability ( et al. ). However, to further reduce the cost of trickling filter system, the self-sustainable support media having less economic values should be used (Ali et al. ). Therefore, the present research study is aimed to develop a simple and efficient trickling filter WWT system with biofilm support media such as maize cob (TF1) and date palm fiber (TF2).
The evaluation of biofilm support media was also accomplished to overcome the impacts of the pollution indicators and to produce good quality effluent which can safely be used for peri-urban agriculture.

Experimental setup
A pilot scale WWT system including two stage trickling fil-

RESULTS AND DISCUSSIONS
The TF1 (maize cob) and TF2 (date palm fiber) were com-  Table 1. BOD is considered as an important parameter used to determine the biodegradation rates of organic contamination load in wastewater (Shah et al. ). The BOD removal rates of TF1 and TF2 are presented in Figure 3.
The mean value of BOD was 151.42 mg/L in the wastewater as an influent and decreased to an average value of 13.68 mg/L 17.4 mg/L and 30.9 mg/L in the effluent of TF1 and TF2, respectively. It presented an average removal rate of the BOD as 87.6% for TF1 and 78.7% for TF2 during the whole 15 weeks operational period. The results show that BOD removal efficiency increased with operational time from the 1st to 15th week and range from 77.4% to 97.5% for TF1 and 67% to 87.1% for TF2 at a flow rate of 7.2 L/min. The highest removal efficiency was recorded as 97.9% at 10th week for TF1 and 87% at 13th week for TF2. However, the TF1 was found more efficient in BOD    TP is a macro-nutrient present in WW in small amounts.
The high TP in wastewater causes eutrophication in water bodies. In the present research, phosphorus removal from TF1 and TF2 was recorded 38.5% and 32.1% respectively ( Figure 6). The effluent TP was found close to the permiss-

CONCLUSIONS
The developed pilot scale  managing not only the regional wastewater pollution but also help a relatively safe re-use of the wastewater for peri urban agriculture and protect our receiving environment.
This is particularly significant in the current water resource shortage scenario in the country and may also help to safe re-use of wastewater for peri-urban food agriculture in Multan region of Pakistan as well as in developing world.

DATA AVAILABILITY STATEMENT
All relevant data are included in the paper or its Supplementary Information.